Fix incorrect XML documentation in database AddDatabase methods for PostgreSQL, MySQL, and SQL Server

[Copilot]

The XML documentation for database AddDatabase methods across PostgreSQL, MySQL, and SQL Server extensions contained misleading or incomplete information about automatic database creation behavior.

The Issue

The PostgreSQL documentation incorrectly stated:

Note that by default calling AddDatabase(IResourceBuilder{PostgresServerResource}, string, string?) does not result in the database being created on the Postgres server. It is expected that code within your solution will create the database.

Meanwhile, MySQL and SQL Server had minimal documentation that didn't explain the database creation behavior at all.

However, the actual implementation in all three providers shows that databases ARE created automatically:

1. All providers subscribe to ResourceReadyEvent/OnResourceReady
2. When the database server becomes ready, they automatically call CreateDatabaseAsync for each database
3. The CreateDatabaseAsync methods execute CREATE DATABASE commands

This is also confirmed by functional tests which successfully connect to databases that were added via AddDatabase.

The Fix

Updated the XML documentation across all three database providers to accurately reflect the actual behavior:

• PostgreSQL: Corrected the misleading documentation
• MySQL: Added comprehensive documentation explaining automatic database creation
• SQL Server: Added comprehensive documentation explaining automatic database creation

All three now consistently document:

Note that calling AddDatabase(...) will result in the database being created on the server when the server becomes ready. The database creation happens automatically as part of the resource lifecycle.

This ensures developers have correct and consistent information about how databases are handled across all .NET Aspire database providers.

Fixes #10858.

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[Copilot]

Pull Request Overview

This PR fixes incorrect XML documentation in the PostgreSQL extension's AddDatabase method. The documentation previously stated that databases are NOT automatically created, which was misleading since the implementation actually does create databases when the server becomes ready.

• Updates XML documentation to correctly reflect that databases WILL be automatically created
• Removes misleading guidance about requiring manual database creation
• Corrects the waitFor behavior documentation

[Copilot]

The updated documentation should clarify when exactly the database creation occurs. Consider adding that it happens during the ResourceReadyEvent to be more specific about the timing.

Suggested change

	/// The database creation happens automatically as part of the resource lifecycle.
	/// Specifically, the database creation occurs during the <c>ResourceReadyEvent</c> as part of the resource lifecycle.

[davidfowl]

@copilot do the same for MySQL and SQL Server

[Copilot]

@copilot do the same for MySQL and SQL Server

I've updated the XML documentation for both MySQL and SQL Server AddDatabase methods to match the PostgreSQL fix. Both now include comprehensive documentation explaining that databases are automatically created when the server becomes ready, just like PostgreSQL. All three database providers now have consistent and accurate documentation about automatic database creation behavior. Changes committed in c60a51f.