Try running full tests on release PRs

[guarani]

This change proposes creating new jobs on CircleCI that will run full tests on release PRs. Previously these changes were optional.

Addresses wordpress-mobile/release-toolkit-gutenberg-mobile#78 (this issue can only be marked resolved when wordpress-mobile/release-toolkit-gutenberg-mobile#79 is also merged)

To test

1. Note that this PR's base branch is of the format release/.*, which should make this PR behave like a release PR in that optional tests should be run automatically.
2. Verify that the full tests suite is ran for both platforms.

This PR currently creates a new job to run the tests. We already have a job, Test Android on Device - Full (Submodule Update), to run tests automatically on Dependabot PRs, but I chose to make a new job to allow customizing the job name to Test Android on Device - Full (Release). If you think it's best to combine these jobs under a more generic name such as Test Android on Device - Full, that's also something we can do.

PR submission checklist:

• I have considered adding unit tests where possible.
• I have considered if this change warrants user-facing release notes more info and have added them to RELEASE-NOTES.txt if necessary.

[geriux]

LGTM! 👏 the full tests for both platforms were run.

I think it's good to have a different job with a different name so it's easier to differentiate. Thanks for improving this @guarani!