chore(Tests workflows): caching one build for Amplify-Package instead of one for each plugin

[ruisebas]

Description

This PR makes the following changes to our unit tests and integration tests workflows:

• Adds the missing targets to the Amplify-Package scheme
• Updates the run_xcodebuild action to support dependencies and previous build caches.
• Creates a new build-amplify-swift workflow that takes a platform and builds the Amplify-Package target and that caches the build folder.
  • This build cache is only saved when the workflow is run in the main branch, and it's the one used by all unit and integration test runs.
• Creates a build-amplify-swift-platform workflow that runs the previous workflow for all our supported platforms.
• Creates a run_unit_tests workflow that runs the unit tests for a scheme and platform, using the Amplify-Package build cache.
• Renames run_xcodebuild_test_platforms to run_unit_tests_platforms, which calls the previous workflow for our targets and platforms.
• Removes all the plugin and SHA specific caches, as they did not really speed things up and just made us frequently run out of cache space.
  • An Amplify-Package cache takes around 600 MB per platform, while the sum of all plugin caches was around 1.5 GB per platform.
• Adds inputs to the unit tests workflows so we can run them only in certain platforms
• Replaces the 'Dummy' values with 'None', as agreed in chore: Adding caching and retries to Integration Tests #3339 (comment)

General Checklist

• Added new tests to cover change, if needed
• Build succeeds with all target using Swift Package Manager
  • Build Amplify Swift
• All unit tests pass
  • Unit Tests | All
• All integration tests pass
  • Integration Tests
  • Integration Tests | API - All
  • Integration Tests | DataStore - All (And in the first attempt!! 😮 )
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)
• Documentation update for the change if required
• PR title conforms to conventional commit style
• New or updated tests include Given When Then inline code documentation and are named accordingly testThing_condition_expectation()
• If breaking change, documentation/changelog update with migration instructions

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