[receiver/mongodb] Add missing replication lag metrics

[RutvikS-crest]

Component(s)

receiver/mongodb

Is your feature request related to a problem? Please describe.

Currently mongodb receiver doesn't have any metric that can be used to get the replication lag stats among replica sets.

Describe the solution you'd like

Utilise flowcontrol document under serverStatus to expose a new metric.

Describe alternatives you've considered

No response

Additional context

No response

[github-actions]

Pinging code owners:

• receiver/mongodb: @djaglowski @schmikei

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[VihasMakwana]

This sounds like a valid enhancement. We already have ServerStatus command in mongodb receiver and we can extend that command to include the flowControl block to metrics.
I'd love to get feedback from codeowners.