The Get service account credentials API now returns file-backed tokens from all
nodes instead of only the local node. For each file-backed service token, we
list names of the nodes where this token is found. The response for node-local
credentials (currently only file-backed tokens) is place inside the
"nodes_credentials.file_tokens" field. There is also a nodes_credentials._nodes
field containing information about the overall request execution (it works the
same way as the _nodes field of Nodes info API, etc.) Detailed response sample
can be found in #74530
This PR also removes the beta label from the API's documentation page.
Resolves: #74530
Yang Wang