Implement env:init, env:load and env:unload commands

[khamilowicz]

Why

Commands streamlining usage of environment variables

• eas env:init - install direnv, set up .envrc file and .gitignore
• eas env:load --environment production - pulls envvars from given environment and loads them
• eas env:unload - unloads envvars

Test Plan

Tested manually

[linear[bot]]

ENG-11920 Add `eas env:push` command

[github-actions[bot]]

Size Change: +10.4 kB (+0.02%)

Total Size: 51.8 MB

Filename	Size	Change
./packages/eas-cli/dist/eas-linux-x64.tar.gz	51.8 MB	+10.4 kB (+0.02%)

_{compressed-size-action}

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 20.20202% with 158 lines in your changes missing coverage. Please review.

Project coverage is 52.28%. Comparing base (fbc3924) to head (dacdfdd). Report is 184 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/eas-cli/src/commands/env/init.ts	10.38%	113 Missing and 8 partials :warning:
packages/eas-cli/src/commands/env/load.ts	34.89%	26 Missing and 2 partials :warning:
packages/eas-cli/src/commands/env/unload.ts	55.00%	9 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2504      +/-   ##
==========================================
- Coverage   52.59%   52.28%   -0.31%     
==========================================
  Files         548      551       +3     
  Lines       20409    20607     +198     
  Branches     4163     4198      +35     
==========================================
+ Hits        10732    10772      +40     
- Misses       8837     8985     +148     
- Partials      840      850      +10     

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[github-actions[bot]]

⏩ The changelog entry check has been skipped since the "no changelog" label is present.