API support for blockchain activity metrics

[He1DAr]

Create an API endpoints to provide key blockchain activity metrics:

• Transaction histogram: number of transactions over time.
• Blocks mined: number of blocks mined.
• Contracts deployed: number of new smart contracts deployed.
• Active addresses: count of unique addresses interacting with the blockchain.

The API should support:

• Start and end data/time range.
• Granularity options (e.g., hourly, daily, weekly) for flexible charting.

related to: hirosystems/explorer#2039