adding nbextension path to voila config object

[dharmaquark]

Code changes

This PR introduces nbextensions_path as a configurable value that we can set to override the default Jupyter Server value (as a workaround until Voila moves away entirely from nbextensions to adopt the lab extension system)

References

Background on Motivation (credit @SylvainCorlay)

While Voilà is built with JupyterLab components, we use the classic notebook extension system for the widgets, because when Voilà came out, JupyterLab could not use pre-built extensions.
By default, Voilà uses the webpack bundles that are published on npmjs.
But in order to support extensions that have never been published, but are installed locally, we added support for using local notebook extensions.
Jupyter server is the raw server, and it does not come with the notebook frontend, hence it does not have a notion of notebook extensions. As a workaround for applications that have a nbextension path different from the default, we are adding an option nbextensions_path to the Voila Configuration object, so that we are not tied to the server default.

User-facing changes

introduces a new optional configuration value that users can set to override default server nbextensions path

Backwards-incompatible changes

N/A

[github-actions]

👈 Launch a Binder on branch dharmaquark/voila/0722-configpath

[SylvainCorlay]

Thanks for making the PR. I am happy to merge as it looks good to me.

[github-actions]

Benchmark report

The execution time (in milliseconds) are grouped by test file, test type and browser.
For each case, the following values are computed: min <- [1st quartile - median - 3rd quartile] -> max.

Results table

Test file	voila-tree-classic.ipynb	voila-tree-light.ipynb	voila-tree-dark.ipynb	voila-tree-miami.ipynb	basics.ipynb	bqplot.ipynb	dashboard.ipynb	gridspecLayout.ipynb	interactive.ipynb	ipympl.ipynb	ipyvolume.ipynb	multiple_widgets.ipynb	query-strings.ipynb	reveal.ipynb
Render
chromium
actual	79 <- [88 - 103 - 128] -> 214	112 <- [128 - 155 - 211] -> 370	96 <- [99 - 119 - 123] -> 151	62 <- [66 - 71 - 81] -> 112	2350 <- [2461 - 2511 - 2579] -> 3090	2312 <- [2390 - 2493 - 2590] -> 3260	2331 <- [2350 - 2358 - 2454] -> 2792	2349 <- [2401 - 2437 - 2577] -> 2638	1668 <- [1696 - 1739 - 1808] -> 2131	3286 <- [3375 - 3497 - 3768] -> 4570	7600 <- [8452 - 8798 - 9001] -> 9021	5630 <- [5729 - 5738 - 5774] -> 5779	1248 <- [1249 - 1289 - 1385] -> 1406	2388 <- [2393 - 2500 - 2601] -> 2826
expected	3379 <- [3442 - 3517 - 3701] -> 3876	2976 <- [3227 - 3321 - 3421] -> 3604	3608 <- [3623 - 3709 - 3793] -> 3825	4453 <- [4453 - 4523 - 4661] -> 4748	2559 <- [2655 - 2656 - 2660] -> 2674	3982 <- [4079 - 4213 - 4356] -> 4743	12183 <- [18509 - 19553 - 20811] -> 21515	15319 <- [15660 - 15796 - 15912] -> 16056	1517 <- [1920 - 1997 - 2103] -> 2113

❗ Test metadata have changed

--- /dev/fd/63	2022-07-13 22:24:25.628446958 +0000
+++ /dev/fd/62	2022-07-13 22:24:25.628446958 +0000
@@ -4,37 +4,37 @@
     "BENCHMARK_REFERENCE": "actual"
   },
   "browsers": {
-    "chromium": "97.0.4666.0"
+    "chromium": "94.0.4595.0"
   },
   "systemInformation": {
     "cpu": {
-      "brand": "Xeon® Platinum 8370C",
+      "brand": "Xeon® E5-2673 v3",
       "cache": {
-        "l1d": 98304,
+        "l1d": 65536,
         "l1i": 65536,
-        "l2": 2097152,
-        "l3": 50331648
+        "l2": 524288,
+        "l3": 31457280
       },
       "cores": 2,
       "family": "6",
-      "flags": "fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ss ht syscall nx pdpe1gb rdtscp lm constant_tsc rep_good nopl xtopology cpuid pni pclmulqdq ssse3 fma cx16 pcid sse4_1 sse4_2 movbe popcnt aes xsave avx f16c rdrand hypervisor lahf_lm abm 3dnowprefetch invpcid_single pti fsgsbase bmi1 hle avx2 smep bmi2 erms invpcid rtm avx512f avx512dq rdseed adx smap clflushopt avx512cd avx512bw avx512vl xsaveopt xsavec xsaves md_clear",
+      "flags": "fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ss ht syscall nx pdpe1gb rdtscp lm constant_tsc rep_good nopl xtopology cpuid pni pclmulqdq ssse3 fma cx16 pcid sse4_1 sse4_2 movbe popcnt aes xsave avx f16c rdrand hypervisor lahf_lm abm invpcid_single pti fsgsbase bmi1 avx2 smep bmi2 erms invpcid xsaveopt md_clear",
       "governor": "",
       "manufacturer": "Intel®",
-      "model": "106",
+      "model": "63",
       "physicalCores": 2,
       "processors": 1,
       "revision": "",
       "socket": "",
-      "speed": 2.8,
+      "speed": 2.4,
       "speedMax": null,
       "speedMin": null,
-      "stepping": "6",
+      "stepping": "2",
       "vendor": "GenuineIntel",
       "virtualization": false,
       "voltage": ""
     },
     "mem": {
-      "total": 7283843072
+      "total": 7291699200
     },
     "osInfo": {
       "arch": "x64",
@@ -42,11 +42,11 @@
       "codename": "Focal Fossa",
       "codepage": "UTF-8",
       "distro": "Ubuntu",
-      "kernel": "5.13.0-1031-azure",
+      "kernel": "5.8.0-1040-azure",
       "logofile": "ubuntu",
       "platform": "linux",
-      "release": "20.04.4 LTS",
-      "serial": "acf9b72ca2cf49f881ae9327accecb1e",
+      "release": "20.04.3 LTS",
+      "serial": "cfc067bfcb844f35865e279a1b0e66c5",
       "servicepack": "",
       "uefi": false
     }