[KOTS]: Add preflight checks to verify DB, Storage, Registry connections

[mrsimonemms]

KOTS doesn't have any native verification for the connections to the external dependencies in the config. Add a series of preflight checks to ensure that the values the user has entered are correct.

• KOTS database preflight checks #9931
• KOTS registry pre-flight checks #10337
• KOTS storage checks #9933

This will likely require some custom container images building to handle our complexity (eg, CloudSQL support for DB). It would be good to export the script anyway so it can be used in the support bundles too