Feat(eos_cli_config_gen): Add support for changing the notification timestamp mode for gnmi

[noredistribution]

Enhancement summary

In 4.27.0F we've added support for changing the notification timestamp from the last-change-time (GNMI spec) to send-time (outside of spec) to support (legacy) systems that don't keep track of the last known state of a counter

Which component of AVD is impacted

eos_cli_config_gen

Use case example

folks who setup streaming via telegraf or any gnmi client to influx or other dbs and plot graphs with grafana won't see states outside of the selected range if that state has not changed for a long time, even if sampling mode is configured, as other systems are not like CloudVision which keeps track of the last known state of each counter...

Describe the solution you would like

we have a new cli "notification timestamp send-time" that can override the ts of the notifications everytime we stream it even if they did not change
ref: https://aristanetworks.github.io/openmgmt/configuration/openconfig/#telemetry-timestamps

Describe alternatives you have considered

No response

Additional context

No response

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