feat: v2.8.0 (db events metric)

[ekjotsinghmakhija]

This pull request introduces changes to improve connection handling, enhance tenant-specific event tracking, and optimize code readability and maintainability. Key updates include adjustments to connection limits, the addition of tenant-based database event tracking, and minor refactoring for consistency.

Connection Handling Updates:

• Updated max_connections in config/runtime.exs to 1000 with additional documentation explaining the calculation of total connections using num_acceptors.
• Adjusted hard_limit and soft_limit in deploy/fly/prod.toml to 100,000 to align with the updated connection handling logic.

Tenant-Specific Database Event Tracking:

• Introduced a db_events_per_second_key function in lib/realtime/tenants.ex to generate keys for tracking database events per tenant.
• Added a start_db_rate_counter function in lib/realtime_web/channels/realtime_channel.ex to initialize counters for tenant-specific database events.
• Integrated the new db_events_per_second_key into the message dispatcher to count database events per tenant. [1] [2]

Code Refactoring and Telemetry Enhancements:

• Removed unused aliases GenCounter and Tenants from lib/extensions/postgres_cdc_rls/replication_poller.ex for clarity.
• Added a new telemetry event [:realtime, :rate_counter, :channel, :db_events] in lib/realtime/telemetry/logger.ex for monitoring database events.