Compare Checksum from `release-*` rather then the PR Branch

[CodeGat]

We currently have to rebase dev-* onto release-* every configuration release, in order to compare the next config update against the one just released. This is because we use the dev-* branches testing/checksum/historical-*hr-checksum.json file to compare against the newly created checksum, as that is the default --checksum-path of model-configs-test.

Now, test-repro.yml can select which branch (or config tag) we want to compare against explicitly, rather than relying on a model-configs-test default.

In this PR:

• Update test-repro.yml to take in a renamed config-tag->config-ref input and a new optional compared-config-ref input, which more explicitly notes that one config-ref will be compared with another, rather than relying on the default --checksum-path of ./testing/checksum/.
• Updated all workflows that refer to the updated test-repro.yml.
• Added comments!
• In https://github.com/ACCESS-NRI/model-config-tests/commit/0646a1ddc7b29a26693ff97331a21074571c7f83, instead of just deleting ${{ env.EXPERIMENT_LOCATION }}/base-experiment and ${{ env.EXPERIMENT_LOCATION }}/test-venv separately, delete everything in ${{ env.EXPERIMENT_LOCATION }}/*. Will need @jo-basevi s opinion on this one before merging!

References #33

[CodeGat]

Note, this PR will need to change based on https://github.com/ACCESS-NRI/model-config-tests/pull/34