Weaveworks rego policies: create a monorepo structure

[fabriziosestito]

Is your feature request related to a problem?

Based on the migration script described here: #805, create a monorepo structure containing the migrated policies.

Solution you'd like

Acceptance criteria

• It should be possible to release policies separately
• It should be possible to upload a single policy to ArtifactHub after it is released
• Document release process on README.md

Nice to have:

• The monorepo CI should be able to run tests on a single policy when changes are detected

Implementation details

Releasing

Given a monorepo with policies in a similar structure:

policies\
   policy1
   policy2
   ...

When a tag with the format policy1/v1.0.2 is created, the automation should be able to release policy1 with version v1.0.2.
This should be easy enough as we will split the tag by / and release the target policy with the target version.
We should use our reusable GitHub actions: https://github.com/kubewarden/github-actions, note that they might need modification to support different paths.

The actions should release the policy on GitHub and change the metadata of the ArtifactHub files. As examples, see artifacthub-pkg.yml and artifacthub-repo.yml on an existing policy repo, such as this monorepo. See also artifacthub-* docs.

Every time we push/open a PR, the tests should be run for only the files/policies changed. This can be achieved by having a script that filters for the files changed with git, exposed via a global makefile target.