Add support for Vector Search Indexes

[alexott]

Changes

This is initial work - right now things are blocked by errors in OpenAPI spec, and as result, Go SDK has incorrect structs. So we need to wait until spec is fixed

Tests

• make test run locally
• relevant change in docs/ folder
• covered with integration tests in internal/acceptance
• relevant acceptance tests are passing
• using Go SDK

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 73.43750% with 17 lines in your changes are missing coverage. Please review.

Project coverage is 83.51%. Comparing base (fdd0fe9) to head (bb7dc9f).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3266      +/-   ##
==========================================
- Coverage   83.56%   83.51%   -0.06%     
==========================================
  Files         177      178       +1     
  Lines       16523    16598      +75     
==========================================
+ Hits        13808    13862      +54     
- Misses       1877     1891      +14     
- Partials      838      845       +7     

Files	Coverage Δ
provider/provider.go	94.70% <100.00%> (+0.02%)	⬆️
vectorsearch/resource_vector_search_endpoint.go	80.76% <ø> (ø)
vectorsearch/resource_vector_search_index.go	73.01% <73.01%> (ø)

... and 2 files with indirect coverage changes

[alexott]

Regarding integration tests - it's not clear how to programmatically pull models from the Marketplace :-(

[alexott]

@mgyucht to add acceptance tests we need to fix a number of issues: #3388, #3383, #3375, plus solve the problem with registration of models from the marketplace...

[mgyucht]

LGTM with two small nits, discussed adding integration test in a follow-up offline.