Make projectPath group-writable

[thitch97]

Summary

Makes the projectPath group-writable at the end of the build phase.

Use Cases

Resolves #355

Checklist

• I have viewed, signed, and submitted the Contributor License Agreement.
• I have linked issue(s) that this PR should close using keywords or the Github UI (See docs)
• I have added an integration test, if necessary.
• I have reviewed the styleguide for guidance on my code quality.
• I'm happy with the commit history on this PR (I have rebased/squashed as needed).

[thitch97]

I have been able to do integration testing on this locally but have opted to hold off on including integration tests here until a consensus is reached on how to properly test stacks with different build and run uids. Separate issue & PR will follow.

[g-suraj]

Anything in particular holding this PR from being approved/merged? Seems like it's good to go

[thitch97]

Anything in particular holding this PR from being approved/merged? Seems like it's good to go

@g-suraj A couple things, yes. My fellow subteam maintainer is out for another week or so and this will require their approval. There were also concerns over whether this approach goes against the intentions of the Secure Runtime Environments RFC in its permissiveness but that isn't necessarily an outright blocker.