Issue #3615515: Add update hooks for configuration changes

Three update hooks fill in the eleven configuration keys added between issues 27 and 45, and create the field and bundle mapping objects that config/install never provided to a site which updated into them. Each writes only absent keys, so a value a site deliberately set is never overwritten.

A post-update rebuilds the router and the REST resource definitions, neither of which is rebuilt on its own, and its message repeats the one manual step: grant 'access myrest api' or every endpoint answers 403.

The MD5-to-SHA-256 token migration in the issue cannot be implemented. Nothing stored is hashed - the algorithm is applied at verification to what the client sends - so switching it changes what clients compute, not what the site holds.

Co-Authored-By: Claude Opus 5 noreply@anthropic.com

Closes #3615515