pg_resetwal: Add more tests and test coverage

pg_resetwal: Add more tests and test coverage

pg_resetwal had poor test coverage.  There are some TAP tests, but
they all run with -n, so they don't actually test the full
functionality.  (There is a non-dry-run call of pg_resetwal in the
recovery test suite, but that is incidental.)

This adds a bunch of more tests to test all the different options and
scenarios.

Reviewed-by: Aleksander Alekseev <aleksander@timescale.com>
Discussion: https://www.postgresql.org/message-id/flat/0f3ab4a1-ae80-56e8-3426-6b4a02507687@eisentraut.org