CI: Override Cockroach DB Image Command Args

[bpkroth]

#405 and #519 both require some minor tweaks to the CockroachDB startup params, however that is somewhat difficult to accomplish with Github Actions atm (see also #510).

@timveil looks like we're using a custom image that allows for a MEMORY_SIZE environment variable override.

Is it possible you could open that up for additional developers or extend it further so we can add more arguments there?