Include image tag in built image

Fixes

Fixes https://github.com/WordPress/openverse-infrastructure/issues/332 by @AetherUnbound

Description

This PR changes the API and API nginx images to include the image tag as a part of the built docker images, so it can be referenced appropriately once the service is deployed without having to alter the ECS task definition every time.

The logic I've added should use the github SHA as the SEMANTIC_VERSION for all pushes to main, but use the ref name (e.g. tag version like "v2.5.10") for all releases.

Testing Instructions

Very hard to test GitHub actions, this is based off of similar work on the frontend so I'm hoping it works!

Checklist

[x] My pull request has a descriptive title (not a vague title like Update index.md).
[x] My pull request targets the default branch of the repository (main) or a parent feature branch.
[x] My commit messages follow [best practices][best_practices].
[x] My code follows the established code style of the repository.
[ ] I added or updated tests for the changes I made (if applicable).
[ ] I added or updated documentation (if applicable).
[ ] I tried running the project locally and verified that there are no visible errors.

[best_practices]: https://git-scm.com/book/en/v2/Distributed-Git-Contributing-to-a-Project#_commit_guidelines

Developer Certificate of Origin

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WordPress / openverse-api