HV-1702 create postgres rotating secret

[keeefer]

Changes proposed in this PR:

Adds support for creating postgres rotating secrets.

How I've tested this PR:

How I expect reviewers to test this PR:

Checklist:

• Tests added if applicable
• CHANGELOG entry added or label 'pr/no-changelog' added to PR

  Run CHANGELOG_PR=<PR number> make changelog/new-entry for guidance
  in authoring a changelog entry, and commit the resulting file, which should
  have a name matching your PR number. Entries should use imperative present
  tense (e.g. Add support for...)

[ncabatoff]

Could you add a test case for postgres?

Also, when I try to create a config interactively:

hcp vs secrets  create --app=app-tgr sec_tgr --secret-type=rotating
✔ postgres
usernames: ***
integration_name: ****
rotation_policy_name: ***
ERROR: error marshaling details config: json: cannot unmarshal string into Go struct field
Secrets20231128PostgresParams.postgres_params.usernames of type []string

• I can't see what I'm typing
• The order in which the fields are given is random
• I don't know how to provide a list of usernames; I tried ["user1", "user2"], among other things

[averche]

Does this allow multiple usernames to be specified?

[ncabatoff]

Isn't PostgresParams returned here too?