Button to clear cache (in dropdown)

[KesterTan]

Description

Added a button to clear expired cache (cache cleanup).

On desktop

On mobile

After button is pressed

Motivation and Context

Previously, an admin had to run the command rake user:cleanup_cache to clear expired cache #1634 . This button makes it easier to do so.

How Has This Been Tested?

Preliminary steps

• Enable caching in development by running rails dev:cache
• In development.rb, replace config.cache_store = :memory_store with config.cache_store = :file_store, "tmp/cache/scores"

Test that rake task clears expired entries

• For testing purposes, change :expires_in and race_condition_ttl to 5.seconds (in all 3 places)
• Load the gradesheet of an assessment (e.g. AutoPopulated / Homework0), observe that the path /tmp/cache/scores is populated
• Wait a few seconds, click Manage Autolab followed by Clear Cache, observe that the (expired) entries are cleared

Test that rake task does not clear unexpired entries

• Change :expires_in and race_condition_ttl back to their original values
• Load the gradesheet of an assessment (e.g. AutoPopulated / Homework0), observe that the path /tmp/cache/scores is populated
• Wait a few seconds, click Manage Autolab followed by Clear Cache, observe that the unexpired entries are not cleared
• As a sanity check, run rake user:clear_cache and observe that the entries are cleared

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have run rubocop for style check. If you haven't, run overcommit --install && overcommit --sign to use pre-commit hook for linting
• My change requires a change to the documentation, which is located at Autolab Docs
• I have updated the documentation accordingly, included in this PR

[damianhxy]

Could you also update the documentation?

Specifically: https://docs.autolabproject.com/installation/troubleshoot/#no-space-left-on-device

[damianhxy]

1. Change method to post since it is not an idempotent operation and is vulnerable to CSRF attacks
2. Improve UX by redirecting to previous page where possible

[damianhxy]

LGTM