refactor for model gallery endpoints - bundle up resources into a
struct, make galleries mutable with some crud endpoints. This is
groundwork required for making efficient use of the new scraper - while
that PR isn't _quite_ ready yet, the goal is to have more, individually
smaller gallery files. Therefore, rather than requiring a full localai
service restart, these new endpoints have been added to make life
easier.
- Adds endpoints to add, list and remove model galleries at runtime
- Adds these endpoints to the Insomnia config
- Minor fix: loading file urls follows symbolic links now
