Create article with workarounds for missing popular features

[divega]

This is an opportunity for us to provide some guidance on how to deal with the absence of some features until we have them. For example:

• Many-to-many: @ajcvickers' blog posts
• TPT: Use composition or TPH, or use views
• Spatial: Use SqlGeography and SqlGeometry or materialize to byte[], and FromSql, function mapping
• Stored procedure mapping: ExecuteSqlCommand, triggers, updatable views, etc.
• Graphical visualization of model: use third-party tools
• Entity splitting: views
• Change tracking proxies
• Missing lifecycle hooks
• Simple logging: simple patterns to hook up logging
• Interception: use diagnostics
• Filtered Include: use conditions and short-circuiting in global filters

It should probably be part of the porting section, although workaround can be used in new applications as well.

Note that this is also not necesesarily for EF6 gaps (e.g. filtered include wasn't there).

[ajcvickers]

See dotnet/efcore#12024 for DiagnosticSource example.