feat: bundle a local version of install.sh

[aslilac]

Closes #13548

This allows users to...

• Install a CLI that is known to have the same version as the server binary
• Install the CLI in air-gapped deployments while still getting to run a simple install script

You run something like...

curl -fsSL https://dev.coder.com/install.sh | sh

...and it'll download a "slim" Coder build (CLI only) from the server (which serves these under paths like /bin/coder-$os-$arch) and install it.

This script is based off of our existing install.sh script, and accepts many of the same arguments, but has been tailored to this narrower use case.

There's also some fancy machinery to insert the correct origin to download the binary from using "text/template"

[mafredri]

This is great, nice work!

[matifali]

Another thing, while testing, I noticed this to be very slow compared to the install script we host on GitHub. It is probably a network-related thing, and our coder server may not have the same bandwidth as the GitHub CDNs.

[mafredri]

@matifali it's (in part) because the command doesn't request compression. We could attempt a compressed transfer, but unfortunately that doesn't support a progress bar.

uncompressed (current)

/ # time curl -fL -o ~/.cache/coder/local_downloads/coder-linux-arm64-v2.18.2-devel+3a81aac31.incomplete -C - https://dev.coder.com/bin/coder-linux-arm64
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 36.2M  100 36.2M    0     0  3983k      0  0:00:09  0:00:09 --:--:-- 6951k
real	0m 9.33s
user	0m 0.41s
sys	0m 0.49s

vs compressed:

/ # time curl --compressed -fL -o ~/.cache/coder/local_downloads/coder-linux-arm64-v2.18.2-devel+3a81aac31.incomplete -C - https://dev.coder.com/bin/coder-linux-arm64
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 12.6M    0 12.6M    0     0  3074k      0 --:--:--  0:00:04 --:--:-- 3204k
real	0m 4.21s
user	0m 0.20s
sys	0m 0.09s

[matifali]

Thanks, @mafredri, for investigating. My concern is that before we decide to make this the default behavior, we should ensure this doesn't cause a degradation in experience. I am fine if we lose the progress in favor of a faster download experience.

I have shared some thoughts here: #16125 (comment)