Related Issue(s):

• fix Link 'label:assets' field type as list stac-pydantic#183 (comment)

Description:

• add validate_extensions setting that enables validation of stac_extensions from submitted STAC objects
  using the stac_pydantic.extensions.validate_extensions utility. Applicable only when TransactionExtension
  is active.
• add validatation extra requirement to install additional dependencies required by extension validation (stac-pydantic does not install requests and jsonschema by default)

Given that these checks do not specifically require pgstac (JSON schema validation of remote extension definitions), it could be moved to the parent stac-fastapi. However, I was not sure how that could be integrated since https://github.com/stac-utils/stac-fastapi/blob/main/stac_fastapi/extensions/stac_fastapi/extensions/core/transaction/client.py only contains some abstract classes. Should a mixin be used, which would be added as base class of ClientValidateMixIn?

PR Checklist:

• pre-commit hooks pass locally
• Tests pass (run make test)
• Documentation has been updated to reflect changes, if applicable, and docs build successfully (run make docs)
• Changes are added to the CHANGELOG.