feat: introduce group policies

[flavio]

Allow multiple Kubewarden policies to be grouped together using an evaluation expression.

This PR poses the bases required to implement https://github.com/kubewarden/rfc/blob/main/rfc/0020-policy-group.md

Part of kubewarden/kubewarden-controller#798

[flavio]

@fabriziosestito thanks for the review, I've addressed all the feedback you gave

[codecov]

Codecov Report

Attention: Patch coverage is 76.31579% with 72 lines in your changes missing coverage. Please review.

Project coverage is 58.45%. Comparing base (d401e67) to head (f5e8b1a).

Files	Patch %	Lines
src/evaluation/evaluation_environment.rs	68.31%	64 Missing ⚠️
src/lib.rs	44.44%	5 Missing ⚠️
src/api/service.rs	94.11%	1 Missing ⚠️
src/config.rs	97.50%	1 Missing ⚠️
src/policy_downloader.rs	95.23%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #814      +/-   ##
==========================================
+ Coverage   54.90%   58.45%   +3.54%     
==========================================
  Files          16       17       +1     
  Lines         765      994     +229     
==========================================
+ Hits          420      581     +161     
- Misses        345      413      +68     

Flag	Coverage Δ
integration-tests	50.55% <66.99%> (+2.71%)	⬆️
unit-tests	34.60% <44.55%> (+2.17%)	⬆️

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[fabriziosestito]

LGTM, just one typo to fix.

Also, the latest commit is not a conventional commit.

[flavio]

@fabriziosestito I've addressed your comment. As for the commit format, I plan to squash all of them into a single commit. I'm not doing semantic git commits right now

[flavio]

I think the current code is doing pretty good. I've implemented all the missing TODOs except for these ones:

• When validating the policy group expression, ensure the returned value is a boolean. The check is not working right now, see the commented unit test. This is not a huge deal, since we will do some validation also on the GroupPolicy CRD. There we will use CEL, which allows us to write this kind of check.
• Validate the policy.yml file: error when we find something that is not covered by our spec

[flavio]

Another update:

Validate policies configuration file

• Be strict during deserialization: error when something unknown is found
• Validate policy names: ensure they do not contain the / symbol

[fabriziosestito]

[flavio]

This is really the last change I'm going to make to this PR. With 31b6539 I've introduced a dedicated Rust type to identify policies. We're no longer using strings.

[fabriziosestito]

LGTM @flavio love the latest commit

[jvanz]

[viccuad]

LGTM!

[flavio]

Last round of cleanups:

• Rename PolicyId to PolicyID
• Config: policy group policies are now stored inside of a key named policies instead of members
• EvaluationEnvironment: introduce builder patter, remove duplication between policies and group policies

[viccuad]

LGTM 🚀