[Feature] Add persistent drop monitor functionality

[arista-hpandya]

Description:

This issue tracks the implementation of the persistent drop monitor feature within the dropmonitor orchagent, as described in the SONiC drop counter monitoring HLD. This feature will enable the monitoring of drop counters against configurable thresholds, triggering syslog entries for persistent drops, enhancing network troubleshooting capabilities.

Tasks:

• Implement the logic to monitor drop counters against configured thresholds.
• Add support for the following configurable parameters:
  • Status (enabled/disabled toggle)
  • Window size (sliding time window in seconds)
  • Drop count threshold (minimum drops per window for an incident)
  • Incident count threshold (minimum incidents to trigger a syslog entry)
• Implement the logic to track incidents within the specified window size.
• Implement the logic to generate syslog entries when the incident count threshold is met.
• Ensure minimal CPU overhead. (Target: Nominal increase of the mean CPU utilization by 1 percentage points or less).
• Verify that the feature has minimal effect on memory usage.

Background:

The persistent drop monitor feature enhances the existing SONiC drop counter functionality by adding the ability to monitor for sustained drop patterns. The dropmonitor orchagent will be responsible for implementing the core logic of this feature, including monitoring drop counters, tracking incidents, and generating syslog entries. The configurations are global and will apply to all configured drop counters on the device.

References:

• Umbrella issue tracking the feature development: Internal drop counter monitoring SONiC#1542
• HLD Documentation of the feature: HLD document for configurable drop counter monitoring SONiC#1912