Buck2 integration test

[palfrey]

Description

As per the buildstream test, related to investigation of #1662

Type of change

Please delete options that aren't relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to
  not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Local testing with the new nix target

Checklist

• Updated documentation if needed
• Tests added/amended
• bazel test //... passes locally
• PR is contained in a single commit, using git amend see some docs

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This change is 

[palfrey]

This is draft still mostly because of the hyper NotConnected errors I'm seeing and the capabilities error out of Buck, so like to get those sorted out before merging.