Update integration docs

[davidfowl]

Update the documentation for Postgres integration, serving as the template for all integrations.

Requested improvements to the integration documentation layout:

1. Minimal Hosting Integration Code: Show only the essential code required for hosting the integration, keeping the main content concise for quick adoption.
2. Advanced Configuration Section: Add a dedicated section for advanced configuration, organized as a nested section in the table of contents (ToC).
3. WithReference Configuration Explanation: Clearly present what configuration is passed to other resources in WithReference.
4. Multi-Language Pivot Example: At the bottom of the integration page, provide a pivot that shows how to consume the connection information using a client library, supporting multiple languages (please specify desired languages or libraries).

This issue starts with Postgres, but all integrations should be updated similarly. Please specify any client libraries or languages that should be prioritized.

[alistairmatthews]

#42 addresses points 1, 2, and 3 above. Working on 4.

[davidfowl]

cc @sebastienros for number 4.

For 3. https://github.com/dotnet/aspire/blob/main/docs/specs/connection-properties.md

Also @sebastienros updated the README https://github.com/dotnet/aspire/tree/main/src/Aspire.Hosting.PostgreSQL#postgresql-server