Introduce Stats API

[trueleo]

Description

Adds stats implementation based on atomic u64 counters. On each event ingestion counter is updated and on every sync parquet file size is added to compressed counter. On call to metadata api for stats it produces a json serializable Stats instance which is copy of metadata stats counter. Stats are synced on every s3 sync cycle and is stored inside parseable.json file.

Changes:

• Stats module with StatsCounter and Stats type
• Define stats handler for Actix
• Update events and metadata method for stats
• Add put_stats requirement for storage trait and provide s3 implementation

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This PR has:

• been tested to ensure log ingestion and log query works.
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added documentation for new or modified features or behaviors.