Add support for defining RDS parameter groups

[gherceg]

https://dimagi.atlassian.net/browse/SAAS-19633

When upgrading postgres via terraform, terraform wants to delete the attached parameter group since it is only referenced by the rds instance, and once upgraded, a new group will be created/attached targeting that new version of postgres.

Ideally, we would first create the new parameter group targeting the new version of postgres, which will then allow us to easily compare the existing parameter group and the new group in the AWS console to see what has changed/new defaults, etc. Once confident, we can then update the engine version and parameter_group at the same time, resulting in a successful upgrade.

This supports both the existing way of defining parameter "in-line" in the rds instance or defining them in a separate parameter group and linking that group to the instance. If both are defined on an instance, an error is raised.

Example usage

rds_instances:

  - identifier: "pgtest-staging"
    instance_type: "db.t3.micro"
    storage: 300
    storage_type: gp3
    multi_az: no
    engine_version: "18.3"
    parameter_group: "pgtest-parameters-v18-staging"

rds_parameter_groups:

  - name: "pgtest-parameters-v18-staging"
    family: "postgres18"
    params:
      rds.force_ssl: 0
      shared_preload_libraries: pg_stat_statements
      track_io_timing: 1

Environments Affected

None