Improve case consistency for initialisms in agent_tracker module
As it is suggested in #468 (closed) to handle the issue in multiple MRs, this MR does not include all of the needed renamings, but only the following:
- Rename connectionsByProjectIdHashKey to connectionsByProjectIDHashKey
- Rename connectionsByAgentIdHashKey to connectionsByAgentIDHashKey
- Rename GetConnectedAgentsByProjectIds to GetConnectedAgentsByProjectIDs
- Rename GetConnectedAgentsByProjectIdsResponse to GetConnectedAgentsByProjectIDsResponse
- Rename GetConnectedAgentsByProjectIdsRequest to GetConnectedAgentsByProjectIDsRequest
See https://go.dev/wiki/CodeReviewComments#initialisms for more information.