Add a yarn clean script for the .angular/cache folder

[artlowel]

Description

Since the upgrade to Angular 13 (#1567), Angular CLI persists its cache in a folder in the project root directory (more info) This improves build speeds, but can lead to hard to debug issues where old dependencies or even project code are still being used even though you've run yarn run clean, or changed that code

This PR adds the removal of that cache dir to the yarn run clean command to prevent those issues

Instructions for Reviewers

• Check that you have an .angular/cache folder in your project root. If you don't, build the project in dev mode, and verify that you do afterwards
• Run yarn run clean
• Check that that cache folder is gone

Checklist

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• My PR is small in size (e.g. less than 1,000 lines of code, not including comments & specs/tests), or I have provided reasons as to why that's not possible.
• My PR passes ESLint validation using yarn lint
• My PR doesn't introduce circular dependencies (verified via yarn check-circ-deps)
• My PR includes TypeDoc comments for all new (or modified) public methods and classes. It also includes TypeDoc for large or complex private methods.
• My PR passes all specs/tests and includes new/updated specs or tests based on the Code Testing Guide.
• If my PR includes new libraries/dependencies (in package.json), I've made sure their licenses align with the DSpace BSD License based on the Licensing of Contributions documentation.
• If my PR includes new features or configurations, I've provided basic technical documentation in the PR itself.
• If my PR fixes an issue ticket, I've linked them together.

[kshepherd]

+1 thanks @artlowel , the .angular/cache folder remained after yarn run clean before applying this PR, and afterwards the cache is correctly cleaned.