Add missing documentation for interceptors

[roji]

Closes #4417
Closes #4726

[Copilot]

Pull request overview

This PR expands and centralizes EF Core interceptor documentation (including materialization interceptors and singleton interceptor guidance) by moving detailed examples into the Interceptors doc and simplifying the EF Core 6.0/7.0 “What’s New” sections to summaries with links.

Changes:

• Adds an “Available interceptors” overview plus new/expanded sections and examples to interceptors.md, including singleton interceptor guidance.
• Reworks EF Core 6.0/7.0 “What’s New” interceptor sections to brief summaries with links to the Interceptors doc.
• Removes several “NewInEFCore6/7” sample source files and their invocations that were primarily used for the previously inlined “What’s New” content.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
samples/core/Miscellaneous/NewInEFCore7/QueryStatisticsLoggerSample.cs	Removes now-duplicated sample formerly in EF7 “What’s New”.
samples/core/Miscellaneous/NewInEFCore7/QueryInterceptionSample.cs	Removes sample now documented via Interceptors page examples.
samples/core/Miscellaneous/NewInEFCore7/OptimisticConcurrencyInterceptionSample.cs	Removes sample now covered in Interceptors documentation.
samples/core/Miscellaneous/NewInEFCore7/LazyConnectionStringSample.cs	Removes sample now covered in Interceptors documentation.
samples/core/Miscellaneous/NewInEFCore7/InjectLoggerSample.cs	Removes sample now covered in Interceptors documentation.
samples/core/Miscellaneous/NewInEFCore7/Program.cs	Stops invoking deleted interceptor samples.
samples/core/Miscellaneous/NewInEFCore6/CommandSourceSample.cs	Removes sample now represented inline + linked to Interceptors doc.
samples/core/Miscellaneous/NewInEFCore6/Program.cs	Stops invoking deleted command-source sample.
entity-framework/core/what-is-new/ef-core-7.0/whatsnew.md	Replaces large interceptor example sections with summaries + links to Interceptors doc.
entity-framework/core/what-is-new/ef-core-6.0/whatsnew.md	Updates command-source section to inline snippet + link to Interceptors doc section.
entity-framework/core/logging-events-diagnostics/interceptors.md	Adds interceptor inventory table, singleton interceptor guidance, and several new example sections.