[PostgREST][PortalDB] Add PostgREST data source for fetching Portal Applications data

[commoddity]

🚨 TODO_IN_THIS_PR

Do not merge until these TODOs are resolved:

• TODO_IN_THIS_PR: Update to published version when Portal DB SDK is released - go.mod

🌿 Summary

Add PostgREST data source support as an alternative to direct PostgreSQL connections for fetching Portal Applications data

🌱 Primary Changes:

• Implement new PostgREST data source driver with JWT authentication
• Add configuration support for both PostgreSQL and PostgREST data sources via DATA_SOURCE_TYPE environment variable
• Integrate Portal DB SDK for PostgREST API communication and data mapping
• Add JWT token generation for secure PostgREST API authentication

🍃 Secondary changes:

• Update documentation with PostgREST configuration and usage instructions
• Add new environment variables for PostgREST configuration (base URL, JWT secret, email, role, timeout)
• Update environment validation to support both data source types
• Add dependency on Portal DB SDK for PostgREST API client generation

💡 New TODOs

New TODOs introduced in this PR:

• TODO_TECHDEBT(@commoddity): Remove this method when direct Postgres data source is removed. - postgrest/driver.go

🛠️ Type of change

Select one or more from the following:

• New feature, functionality or library