Find and handle undeclared policy keys

The problem

[10] pry(main)> Ability.allowed?(user, :something_obviously_not_existing, project)
=> false
[11] pry(main)> Ability.allowed?(user, :read_project, project)
=> true

by default you're not allowed to :set_mattress_on_fire or :ride_tricycle_on_roof, or whatever wacky abilities a user asks, seems legit

This was discovered by trying to find the policy override_project_member which appears to have never existed and hid in the codebase since ~2017. Are there other nonexistent keys we don't know about?

Context

See https://gitlab.slack.com/archives/C8HG8D9MY/p1659484641598259 for slack thread (internal, valid 90 days) and !81393 (comment 1048338372) for context.

Possible fixes

Some options

1. Do nothing. Continue to return false to any policy check where the key isn't defined
2. Raise an error if a policy key can't be found
3. Log if a key can't be found
4. something else...?