Clarify docs on --locality-advertise-addr

[jseldess]

Jesse Seldess commented:

This flag is used in a cross-cloud or hybrid scenario where you want nodes in the same region/env to use their internal addresses to communication and nodes on other places to use a public address.

Clarify that the flag is a list of rules with first-match-wins, so you only want to specify the locality level that determines access to the private IP (typically region=us-east1). See cockroachdb/cockroach#42741 for more details.

Jira Issue: DOC-377

[jseldess]

https://www.cockroachlabs.com/docs/v19.2/start-a-node.html#networking.

@taroface, no need to act on this right away. Probably need to let the linked issue resolve first. This will be more important once we write guidance/tutorials on multi-cloud deployment.

[daniel-crlabs]

This came up again today, created a new docs issue since the one from 4 years ago has not been touched: https://cockroachlabs.atlassian.net/browse/DOC-9161

[shralex]

@mdlinville can we prioritize this or the linked docs changes request ? I think a clarification in the docs is needed because the behavior of this flag isn't intuitive, unless one looks at the code.