Rename name templates to validation templates

[JoeZiminski]

This PR renames Name templates to Validation templates (these are custom templates that can be validated against). Name templates is unfinformative as a name so it needs to be changed

Unfortunately it is used in many places across the codebase, including in the configs. Therefore, a new entry into the config-loader is created to find "name_template" as an entry and convert it to "validation_template".

The docs are also updated.

TODO:

1. change the TUI from `template validation" to "validation templates" and update the image on the docs accordingly
2. Do a once-through manual test (CI tests should cover everything but this is a big change touching many places)
3. Check that backward compatibility tests are properly updated.
4. First merge Update documentation: new images, better links to API. #591