postgresql_db: add session_role support for raw connections

[gspanos]

SUMMARY

Fixes #864

Fixes postgresql_db "session_role" behavior when state is dump/restore for binary (.pgc) archives.
It was being ignored but now it behaves as intended by pg_dump/pg_restore

ISSUE TYPE

• Bugfix Pull Request

COMPONENT NAME

postgresql_db

ADDITIONAL INFORMATION

When pg_dump is used, the --role parameter is used to switch to a different user/role that has sufficient permissions to perform the dump.

When pg_restore is used, the --role parameter, in combination with --no-owner, allows you to restore the objects contained in the archive under new ownership (the one specified with --role).

Up to now, whenever pg_dump/pg_restore was used, the session_role parameter was being ignored and it would give surprising results (or errors).

Now the session_role below will be relayed as the --role parameter for pg_dump/pg_restore.

- name: pg_restore archive on dst_db with session_role
  postgresql_db:
    login_user: postgres
    name: dst_db
    state: restore
    target: /tmp/archive.pgc
    session_role: restoration_role
    target_opts: "--no-owner"

I chose to create a new test python module for this feature, as it seemed cleaner and less intrusive with regards to the current integration tests.

[Andersson007]

@gspanos thanks for the fix! LGTM
Could you please:

• add a changelog fragment
• mark it as "ready for review" when it's ready. now it's still a draft

Thanks

[Andersson007]

@gspanos @hunleyd @andreasscherbaum thanks for the contribution!