feat: sync metrics with memgraph counters/gauges/histograms

[imilinovic]

Align the exporter with the current memgraph event definitions: add missing index, operator, transaction, constraint, schema/storage info and memory metrics; refresh HA RPC timers and counters; drop entries that no longer exist in memgraph.

Documentation checklist

• Add the documentation label tag
• Add the bug / feature label tag
• Write a release note, including added/changed clauses
  • Added missing Memgraph counters/gauges/histograms (Constraint, SchemaInfo, StorageInfo, Memory groups plus new Index/Operator/Transaction/HA entries) and changed stale names to match upstream (AppendDeltasRpc → PrepareCommitRpc, ScanAllByLabelProperty* → ScanAllByLabelPropertiesOperator). #33
  • Missing metric groups from older Memgraph versions are now tolerated instead of aborting the scrape. #33
• Link the documentation PR here
  • PR1623 (metrics were out of date in docs as well)
• Tag someone from docs team in the comments