Add a command to delete the cache

[shamazmazum]

Description

This PR adds a command clear-cache for cache deletion.

Checklist:

• Git branch state is mergable.
• Changelog is up to date (via a separate commit).
• New dependencies are accounted for.
• Documentation is up to date.
• Compilation and tests ((asdf:test-system :nyxt/<renderer>))
  • No new compilation warnings.
  • Tests are sufficient.

[aadcg]

@shamazmazum I'd rather not merge these kind of changes until the ffi method is also specialized for Electron.

If I change my mind, the absolute minimum requirement would be for the command to raise a warning when *renderer* is Electron since it is a no-op.

[shamazmazum]

No problem! Doesn't electron allow applications to control their cache?

Tried to use it on FreeBSD, but JS part seems to be too Linux-specific :)

[aadcg]

No problem! Doesn't electron allow applications to control their cache?

It sure does, see https://www.electronjs.org/docs/latest/api/session#sesclearcache.

It would need to be added to cl-electron first, and then to Nyxt.