[release-v2.6] [TraceQL Metrics] Remove all obsolete settings and code for RF3 metrics

[joe-elliott]

Backport 43d9326 from #3995

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What this PR does:
Deletes all obsolete settings and code for metrics queries against RF3 blocks. This path didn't scale, so we pivoted in the last release to a read path using RF1 blocks flushed from the generators. These don't need deduping or complex job handling, and it scales really well. This is the long-term duration, and some of the RF3 path is already broken accidentally by other feature additions, so it's good to delete it now.

This introduces some breaking changes against main builds in the past few months. (There is no breaking change with v2.5, these are unreleased features changing pre-2.6)

1. the rf1_read_path frontend setting is deleted. The read path is always rf1 now. This will cause a configuration parse error on startup if you have set this value. It must be removed.
2. The local-blocks processor must be enabled to start using metrics queries like { } | rate(). If not enabled metrics queries fail with the error localblocks processor not found. Enabling the local-blocks processor can be done two ways:

(a) . Per-tenant in the per-tenant overrides:

overrides:
  'tenantID':
    metrics_generator_processors:
      - local-blocks

(b) or by default for all tenants in the main config:

overrides:
  defaults:
    metrics_generator:
      processors: [local-blocks] 

3. The get metrics queries on historical data, you must configure the local-blocks processor to flush rf1 blocks to object storage:

metrics_generator:
  processor:
    local_blocks:
      flush_to_storage: true

Other changes:

1. The query hints sample and job_interval are obsolete and were only parts of the RF3 sharding mechanism. These hints no longer do anything.

Which issue(s) this PR fixes:
Fixes n/a

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]