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", for backwards compatability. The name is also updated in the TUI.

Tests and docs are also updated. Note SonarCloud is failing, but it is safe to ignore in this case.,

[viktorpm]

I checked out the branch locally and tried creating a validation template. Everything seems to be working as expected.
A few comments and suggestions:

• This sentence is a bit confusing:

  A 'Template' can be set check subject or session names are formatted in a specific way.

  suggestion:

  You can define a custom “Template” to make sure subject or session names follow a particular pattern or format.

• Not sure if SonarCloud Code Analysis test is important, but it failed

• Missing closing bracket (might already be fixed in the rebuilt site):

[viktorpm]

All looks good. I added a few general comments