test: checks that bitcoin-cli autocomplete is in sync

Adds a functional test that parses available RPC commands, generates the associated bitcoin-cli autocomplete file and checks that the current autocomplete file matches.

An outdated autocomplete file can be updated via the --overwrite test parameter.

The first commit syncs the auto-completion file with the current master. The second commits adds the test. It just changes the header of the autocomplete file and moves it to test/functional/data/completion/bitcoin-cli.bash-completion (plus for ease of use and backward compatibility a symlink from contrib/bitcoin-cli.bash-completion to the moved file is created).

This PR aims to fix: https://github.com/bitcoin/bitcoin/issues/17289