Correct the use of connections strings in integration documents

[alistairmatthews]

Although in the Dashboard there is often an environment variable such as ConnectionStrings__postgresdb listed, this shouldn't be used in .NET code for two reasons:

• The double-underscore returns null and should be replaced with a colon.
• We should always encourage the Aspire method instead: var connectionUri = builder.Configuration.GetConnectionString("postgresdb");

The double-underscore version is correct for Python and JavaScript examples.

Fixes: #312

[Copilot]

Pull request overview

This PR corrects the documentation for database integration by removing incorrect references to ConnectionStrings__<name> environment variables and replacing them with the proper Aspire method GetConnectionString("<name>"). The double-underscore format doesn't work correctly and should not be recommended to developers.

Changes:

• Updated C# code examples to use GetConnectionString() instead of GetValue<string>("ConnectionStrings__<name>")
• Removed ConnectionStrings__<name> from environment variable lists in various integration documentation files
• Removed entire documentation sections that demonstrated the incorrect pattern

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
qdrant-host.mdx	Removes incorrect ConnectionStrings__qdrant from environment variable list
qdrant-get-started.mdx	Updates C# example to use GetConnectionString and removes Python/JavaScript examples with incorrect pattern
mongodb-host.mdx	Removes ConnectionStrings__mongodb from environment variable list
milvus-host.mdx	Removes ConnectionStrings__milvusdb from environment variable list
milvus-get-started.mdx	Updates C# example to use GetConnectionString with var keyword
elasticsearch-get-started.mdx	Removes entire section about injected Elasticsearch properties
sql-server-client.mdx	Removes ConnectionString property from documentation table and environment variable list
postgresql-client.mdx	Removes ConnectionString from table and updates explanatory text
oracle-host.mdx	Removes ConnectionStrings__oracledb from environment variable list
mysql-get-started.mdx	Updates C# example to use GetConnectionString with var keyword

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[IEvangelist]

Is this true? I thought connection strings were still present.

[alistairmatthews]

Closing to re-trigger checks.