mod_admin_shell: Add debug:async() command to show blocked async runners

util.async: Expose default runner function This is purely for informational purposes, so it's possible to determine externally whether a runner is using the default runner function (which executes functions as work items) or a custom runner function.

util.async: Record current work item in the runner object Mostly expected to be useful for debugging purposes.

util.async: Improve debug logging in a few places Knowing the state of the coroutine as well as the runner state can be helpful.

util.async: Export a table of currently-waiting runners This can be used for debugging and introspection.

util.poll: Return early if given zero timeout and no pending events Should have been part of f33887f925e1 to ensure it won't skip processing timers at all when very busy.

moduleapi: Update Teal spec Updates for 65fb0d7a2312::59c3d775c7fa

util.prosodyctl.check: Disable https cert check if http_external_url set This would indicate that a reverse proxy is used, which gets to be responsible for that since it probably holds the actual cert.

util.prosodyctl.check: Check cert for HTTPS if http module enabled

util.prosodyctl.check: Update conditions for s2s cert checks The 'anonymous_login' setting is deprecated and prosodyctl check config will tell you to change it to 'authentication = "internal_hashed"', so we shouldn't need to care about here anymore.