Add support for DRAC clusters to the `mila code` command [MT-71]

[lebrice]

This PR:

• adds a new --cluster flag to the mila code command.
• When using --cluster with a cluster that is not known to have internet access on its compute nodes, this also copies any missing vscode extensions from the local machine over to the cluster.
  • (note: this is done asynchronously in the background while waiting on the job to be scheduled, and might continue even after the job is allocated and the vscode window is opened. Seems to work fine as far as I can tell even in that case)
• Adapts the check for the disk-quota on $HOME (/home on Narval, /home/mila on Mila).
• Gives a helpful error message if users don't add --alloc --account=(professor)-ad-gpu (or similar) when using mila code <path> --cluster <some_cluster> (the DRAC account of Mila profs are not hard-coded in the source code).
• Adds tests for the synchronization of vscode extensions as well as other previously-untested parts of the codebase.

TODOs:

• [x] Test it out on all the DRAC clusters, starting from a clean configuration (vscode has not been used on that cluster before).
• [x] Test it out on a Windows machine

[codecov-commenter]

Codecov Report

Attention: 37 lines in your changes are missing coverage. Please review.

Comparison is base (aa953ab) 58.50% compared to head (5090f12) 60.48%.

Files	Patch %	Lines
milatools/cli/commands.py	9.09%	30 Missing :warning:
milatools/cli/utils.py	83.33%	4 Missing :warning:
milatools/cli/vscode_utils.py	94.44%	3 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #85 +/- ## ========================================== + Coverage 58.50% 60.48% +1.97% ========================================== Files 9 9 Lines 1270 1364 +94 ========================================== + Hits 743 825 +82 - Misses 527 539 +12 ``` | [Flag](https://app.codecov.io/gh/mila-iqia/milatools/pull/85/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mila-iqia) | Coverage Δ | | |---|---|---| | [integrationtests](https://app.codecov.io/gh/mila-iqia/milatools/pull/85/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mila-iqia) | `11.36% <11.96%> (?)` | | | [unittests](https://app.codecov.io/gh/mila-iqia/milatools/pull/85/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mila-iqia) | `60.48% <68.37%> (+1.97%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mila-iqia#carryforward-flags-in-the-pull-request-comment) to find out more.

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