Port Groovy Classloader Clearing script to ScriptRunner for Confluence

ScriptRunner for Jira has a built-in script that clears the Groovy Classloader.
https://scriptrunner.adaptavist.com/latest/jira/builtin-scripts.html#_clear_jira_or_groovy_caches

This is often useful in troubleshooting bugs (e.g. SRPLAT-560). It would be good to port this to ScriptRunner for Confluence.

The Jira caches that get cleared may have equivalents in Confluence, though this should really be a separate script.

Acceptance Criteria: As a Confluence admin, I can use a built-in script to clear the Groovy classloader cache.