Introduce GetCommits for batch resolving commits

[marcsanmi]

Context

The current GetCommit API resolves a single commit at a time using the GitHub API. This means that if a profile contains N different versions, the frontend must make N separate requests to retrieve information about each commit. This creates significant network overhead, which could be avoided if the GetCommit API could accept a list of commit references and resolve them all in parallel before responding to the frontend.

The backend has already been updated to support resolving multiple commits at once (see: grafana/pyroscope#3529) by introducing a new GetCommits endpoint.

Action Required

The fronted needs to be updated to leverage this new capability.