feat(alloydb): added PSC config, PSC interface config, PSC instance c…

…onfig (#9184)

- [ ] Regenerate this pull request now.

feat: added two boolean fields satisfies_pzi and satisfies_pzs
feat: added instance network config
feat: added ListDatabases API and Database object
feat: changed field network in NetworkConfig from required to optional
docs: clarified read pool config is for read pool type instances

PiperOrigin-RevId: 591902051

Source-Link: https://togithub.com/googleapis/googleapis/commit/5e74f9dffc391e8660d495a86a8871be338f501d

Source-Link: https://togithub.com/googleapis/googleapis-gen/commit/be1a83a2d59d4ac303271db236f3cc229d804415
Copy-Tag: eyJwIjoiLmdpdGh1Yi8uT3dsQm90LnlhbWwiLCJoIjoiYmUxYTgzYTJkNTlkNGFjMzAzMjcxZGIyMzZmM2NjMjI5ZDgwNDQxNSJ9