feat: adopt gha-scala-library-release-workflow

[tjsilver]

Co-authored-by: @rtyley

What does this change?

Adds the Scala release workflow.

How to test

Post-merge, run the release workflow as per the instructions.

How can we measure success?

This really improves the release process for this library, and should make it a lot easier to make a release.

[rtyley]

I wasn't even certain if this library was actually used anywhere, but doing a GitHub search, I did find:

• https://github.com/guardian/content-api/blob/2c11e6ef5148eb487f3cc2a61528aa846f7591f1/concierge/build.sbt#L48 (I double-checked this one - the project does fail to compile if the "com.gu" %% "configuration" dependency is removed)
• https://github.com/guardian/daily-edition/blob/31db784f5cc64f325d3a90d73361c43ac48cc58a/build.sbt#L28
• https://github.com/guardian/discussion-api/blob/81154e174672656970d281fc53d1dac1ce0259be/discussion-api/build.sbt#L24

All of these users should probably transition off this library, but until they do, it's nice to know we can release a new version with a security patch if we have to!