Add blob-store-stats telemetry device and tests

[b-deam]

This commit adds a new blob-store-stats telemetry device that based on the sample rate collects per-cluster, and per-node blob store statistics as they are reported by the respective API.

You can test this yourself with:

$ esrally race [...] --telemetry='blob-store-stats'

And then checking in the configured remote metrics store:

Notes:

• This is intentionally unlisted from esrally list telemetry given the elevated privileges required to collect these metrics
  • Running without the correct privleges will show:

    elasticsearch.NotFoundError: NotFoundError(404, 'Request for uri [/_internal/blob_store/stats] with method [GET] exists but is not available when running in serverless mode', 'Request for uri [/_internal/blob_store/stats] with method [GET] exists but is not available when running in serverless mode')

• The API doesn't return node names, only IDs. Refactoring the existing metadata collection or adding a separate call to the Info API to allow us to do lookups seems like overkill here

[b-deam]

My tests with --telemetry=blob-store-stats don't show Rally recording results to the metrics store just yet.

Hmm, mine is working.. can you try filtering for name: blob-store-stats on the rally-metrics* index pattern?

esrally race --pipeline=benchmark-only --telemetry='node-stats, recovery-stats, segment-stats, shard-stats, "blob-store-stats]: