Update fb-provider-collateral-api.yaml

[klevi23]

Hi Yaniv,
Following your remarks on this PR, I’ve implemented all four corrections you highlighted:

1. Removed x-tagGroups:

   • You noted that tag groups haven’t been used until now and shouldn’t be introduced in this repo.
   • I completely removed them from the file — there are now only plain tags definitions.

2. Renamed tags to match identifier style:

   • You asked to use identifier-style names (offExchange and collateralWebhooks) instead of spaced names.
   • Updated both tags accordingly for consistent naming across all specs.

3. Clarified the purpose of new tags:

   • You asked about the point of adding tags without corresponding endpoints.
   • I kept the tag definitions in the Collateral API file purely descriptive and removed any placeholder usage, so the tags exist only where they are actually applied.

4. Moved edits to the correct source file:

   • You pointed out that fb-unified-openapi.yaml is auto- generated and that structural changes should be made in fb- provider-collateral-api.yaml.
   • I made all updates directly there, ensuring the unified spec will generate properly.