Add devcontainer support

[AndrewJDawes]

Hey, @winor30 !

This adds support for a local development environment with pnpm using development containers. I found it useful for installing pnpm packages and running integration tests locally before creating a PR.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.11%. Comparing base (8a69841) to head (1537d5b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #46   +/-   ##
=======================================
  Coverage   90.11%   90.11%           
=======================================
  Files          32       32           
  Lines        1244     1244           
  Branches      155      155           
=======================================
  Hits         1121     1121           
  Misses        123      123           

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