feat(app): add lists of adoptable and mandatory project fields

[cmatsuoka]

Project variables are defined in the application metadata and correspond to fields in the project model that can be set using craftctl.

Mandatory adoptable fields are project fields that can be adopted from external sources, including craftctl and metadata files.

Signed-off-by: Claudio Matsuoka claudio.matsuoka@canonical.com

• [x] Have you followed the guidelines for contributing?
• [x] Have you signed the CLA?
• [ ] Have you successfully run tox?

---

[syu-w]

I still got

E   pydantic.error_wrappers.ValidationError: 1 validation error for Project
E   __root__
E     'adopt-info' does not reference a valid part. (type=value_error)

[cmatsuoka]

Rebased on main.

[cmatsuoka]

E pydantic.error_wrappers.ValidationError: 1 validation error for Project E root E 'adopt-info' does not reference a valid part. (type=value_error)

This PR needs to land for canonical/snapcraft#4601 to land on snapcraft, to address all those issues.

[cmatsuoka]

Restacked on top of cherry-picked #217 and #227.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 89.29%. Comparing base (0705676) to head (49a8692). Report is 45 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #231 +/- ## ========================================== - Coverage 99.28% 89.29% -9.99% ========================================== Files 29 47 +18 Lines 1265 2383 +1118 Branches 209 411 +202 ========================================== + Hits 1256 2128 +872 - Misses 6 212 +206 - Partials 3 43 +40 ```

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