Updating Postgres Documentation

[aldrickdev]

What does this PR do? What is the motivation?

This PR will update our Postgres documentation to have similar language across each of the Postgres instructions and adds the missing Operator documentation.

Merge instructions

Merge readiness:

• Ready for merge

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Additional notes

[github-actions]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/aldrick.castro/postgres-adding-operator-docs/database_monitoring/setup_postgres/alloydb
• https://docs-staging.datadoghq.com/aldrick.castro/postgres-adding-operator-docs/database_monitoring/setup_postgres/aurora
• https://docs-staging.datadoghq.com/aldrick.castro/postgres-adding-operator-docs/database_monitoring/setup_postgres/azure
• https://docs-staging.datadoghq.com/aldrick.castro/postgres-adding-operator-docs/database_monitoring/setup_postgres/gcsql
• https://docs-staging.datadoghq.com/aldrick.castro/postgres-adding-operator-docs/database_monitoring/setup_postgres/rds/
• https://docs-staging.datadoghq.com/aldrick.castro/postgres-adding-operator-docs/database_monitoring/setup_postgres/selfhosted

[hestonhoffman]

Looks good! Left a couple of minor edits