Add docker image caching for Gradle github actions workflow

[mikaylathompson]

Description

This PR follows #698, which added docker image caching for the e2e tests pipeline. That has had a few days of bake time and has been working well, so this adds it to the gradle build and test workflow.

As mentioned in the JIRA task, one important consideration is that the cache key for this workflow is the same as for the e2e tests so that the cache can be shared. This is pretty straightforward because both workflows have the same first few steps, so I'm using exactly the same caching step and have verified that the results are the same (see my testing PR below).

Issues Resolved

MIGRATION-1766

Testing

Manual, including in mikaylathompson#2

Check List

• New functionality includes testing
  • All tests pass, including unit test, integration test and doctest
• New functionality has been documented
• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 63.29%. Comparing base (669f0f9) to head (16c735b).
Report is 1 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #716      +/-   ##
============================================
+ Coverage     63.24%   63.29%   +0.04%     
- Complexity     1578     1579       +1     
============================================
  Files           220      220              
  Lines          9156     9156              
  Branches        793      793              
============================================
+ Hits           5791     5795       +4     
+ Misses         2956     2950       -6     
- Partials        409      411       +2     

Flag	Coverage Δ
unittests	63.29% <ø> (+0.04%)	⬆️

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