Fix (HL API) - Add missing UUID property for CustomAsset schema

[RomainLvr]

Checklist before requesting a review

Please delete options that are not relevant.

• I have read the CONTRIBUTING document.
• I have performed a self-review of my code.
• I have added tests that prove my fix is effective or that my feature works.
• This change requires a documentation update.

Description

• It fixes !40022
• Here is a brief description of what this PR does

The UUID property of custom Assets is missing when making a GET call via the HL API. This PR adds the missing property to the schema.

Note: I have a question about the value of the x-version-introduced attribute. Curtis may be able to confirm.

[cconard96]

Some additional changes will be needed for bumping the API version but unless tests fail, I could do it in another PR:

• Router::API_VERSION needs updated to 2.2.0. It should always match the latest version.
• Router::getAPIVersions() array needs updated to include the new minor version
• A snapshot for v2.2.0 will need added to the tests/fixtures/hlapi/snapshots folder. These snapshots are the OpenAPI schema from /api.php/v2.2/doc,json while logged in as a user with full permissions and used to ensure the schema does not change in unexpected ways within a minor version. Ideally, this would be done just before release as changes are expected during the development of the new version.