Audit/update docs: prefixing extension and local type directories

[phazonoverload]

Many extension building guides still reference the need to put extensions in local type directories and prefix the directory with directus-extension-

Audit and update these

[rijkvanzanten]

@phazonoverload Mind adding a description to this one?

[linear]

EDU-352 Audit/update docs: prefixing extension and local type directories