Add environment variables and secrets

[spoenemann]

Closes #537, closes #680.

• New EnvironmentSecret/EnvironmentVariable model classes
• Extended Environment with a repo_name bridging field, nested secrets/variables lists, get_model_objects, resolve_secrets/copy_secrets, and a generate_live_patch override that cascades to nested secrets/variables
• New REST client methods for GET/PUT/DELETE environment secrets and GET/POST/PATCH/DELETE environment variables, plus facade wrappers
• Repository.get_environment() helper and cascading resolve_secrets/copy_secrets
• New JsonnetConfig entries/default-config properties, jsonnet template functions, and JSON schema files
• Web UI resource registry entries
• New unit tests plus new integration tests with extended ModelForContext test helper
• Docs: New pages for environment variables/secrets

[heurtematte]

Thanks for your contribution!

At first glance, it seems that this PR may overlap with this one: #614

Could you clarify the main difference between the two approaches? besides the naming convention.

I'm currently reviewing the other one, maybe worth giving your opinion on this one.

[netomi]

there is also #641 which only adds support for prevent_self_review. We should keep PRs minimal to make it easier to review and test, I would be in favor of merging the other PR first and then update this accordingly.

Edit: I applied the same missing transformation for the new prevent_self_review field from this PR to the other one, added some additional validation and merged it after testing.

[spoenemann]

Ok sorry, I didn't see the previous PRs.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[netomi]

I tried to push some changes but it was not permitted, recreated the PR as #689.

The PR is very good and I would like to get this integrated as is with these slight modifications.