Add removable-media interface plug declaration to the snap packaging(#1618)

[brlin-tw]

Allow snap users to process YAML documents under /media or /mnt paths after connecting to the removable-media snapd slot:

sudo snap connect yq:removable-media

Fixes #1618.

[brlin-tw]

I am able to build a snap from the branch and verify that the patch resolves the issue:

$ git clone --branch=patch-1 https://github.com/brlin-tw/yq.git 'yq - A portable command-line YAML, JSON, XML, CSV, TOML and properties processor'

$ cd 'yq - A portable command-line YAML, JSON, XML, CSV, TOML and properties processor'

$ snapcraft --use-lxd
...stripped...
Snapping |                                                                                                                                                                                                                           
Snapped yq_v4.33.1_amd64.snap
$ sudo snap install --dangerous yq_v4.33.1_amd64.snap 
yq v4.33.1 已安裝

$ sudo snap connect yq:removable-media 
將 yq:removable-media 連接到 snapd:removable-media

$ yq e '.any' /mnt/data1.yml
yaml file should do

Here's a copy for anyone that may be interested in trying with: yq_v4.33.1_amd64.snap.zip

Note that the snap still has access to your $HOME directory and {/mnt,/media} directories, don't install it in your production system without a security audit.