[Feature Request] Provide an API to wait for the index creation

[AlekSi]

Purpose of the feature.
Currently, there is no non-internal API for waiting for the index creation; the usage documentdb_api.create_indexes_background's result is undocumented. FerretDB has to use an internal documentdb_api_internal.create_indexes_non_concurrently API.

Describe the solution you'd like
There is a non-internal documented API for that.
Alternatively, there is a non-internal documented API for creating indexes in the foreground.

Describe alternatives you've considered
Continue using the internal API.
Use documentdb_api_internal.check_build_index_status, which is also internal and not documented.

Additional context
None.

[safern]

cc: @amitprabhudesai

[safern]

We've decided to move check_build_index_status to the public schema to be able to wait on the foreground for a background index build rather than exposing the create_indexes_non_concurrently which needs to hold a connection and could be long running operation and we have been moving away from it slowly.

FYI: @visridha

[AlekSi]

Please make sure that this API is something we can actually use. Right now, it has some opaque parameters.

[safern]

Assigning @amitprabhudesai as this is useless until we fix:
#36

[AlekSi]

Do we know how the API will look like?