Add secondary poll factor to flex counter infra

[apoorv-arista]

HLD Link : fec-flr-hld

What I did

Added a secondary poll factor (FLR interval factor) feature to the flex counter infrastructure for port counters. This introduces a new flr-interval-factor command to the counterpoll utility.

How I did it

• Added a new CLI command flr-interval-factor under the port counter configuration that accepts an integer factor (minimum value of 1)
• Implemented a flr_interval_factor() function in counterpoll/main.py that sets the SECONDARY_POLL_FACTOR in the ConfigDB's FLEX_COUNTER_TABLE for PORT entries
• Modified the show() function to display the secondary poll factor when it's configured

How to verify it

1. Configure the FLR interval factor using the command:

   counterpoll port flr-interval-factor <factor>

[mssonicbld]

/azp run

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