[improve][broker] Implemets PIP-487: add event count metrics for InflightReadsLimiter acquire and release operations

[poorbarcode]

Motivation & Modifications

See #26092

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment