Cherry-picked d2528b26b6

Conflicts:
- `app/serializers/initial_state_serializer.rb`:
  Upstream changed stuff, we had extra attributes.
  Applied upstream changes while keeping our extra attributes.
- `app/serializers/rest/instance_serializer.rb`:
  Upstream actually moved that to `app/serializers/rest/v1/instance_serializer.rb`,
  so updated that file by keeping our extra attributes, and took upstream's
  version of `app/serializers/rest/instance_serializer.rb`.
- `spec/views/about/show.html.haml_spec.rb`:
  Took upstream's version.

* Bump active_model_serializers from 0.10.9 to 0.10.10

Bumps [active_model_serializers](https://github.com/rails-api/active_model_serializers) from 0.10.9 to 0.10.10.
- [Release notes](https://github.com/rails-api/active_model_serializers/releases)
- [Changelog](https://github.com/rails-api/active_model_serializers/blob/v0.10.10/CHANGELOG.md)
- [Commits](https://github.com/rails-api/active_model_serializers/compare/v0.10.9...v0.10.10)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

* Add root option to render method

Fixes #10652

* Move ApiController to Api/BaseController

* API controllers inherit from Api::BaseController

* Add coverage for various error cases in api/base controller