Postgres: Decouple plugin from core grafana

[gwdawson]

decouple the postgres datasource plugin.

for a howto please see the related internal documentation.

Tasks

• SQL: remove from-grafana-core imports, except setting for postgres #77632
• postgresql: change plugin id #77444
• SQL: extract shared javascript code from core grafana #78617
• SQL: extract shared go code from core grafana #78618
• postgres: remove from-core import of setting #83561
  • probably blocked by postgres: switch to the pgx go module #87037
• postgres: prepare decoupled backend and plugin.json #87039
  • blocked by postgres: remove from-core import of setting #83561
• postgres: prepare decoupled frontend #87040