[WIP] SQS mode: prometheus add nodes gauge

[phuhung273]

Issue #, if available:
#785

Description of changes:

• Count nodes being tracked

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[phuhung273]

@stevehipwell can you please give me a help on this. Now i only stuck at writing unit test for opentelemetry.go since it doesn
t have any test.

Do you think i should refactor this file along with this PR or should I open another separate PR (eg: make opentelemetry.go testable)

[stevehipwell]

@phuhung273 I'm not a maintainer here but I like to see untestable code refactored to be testable, following the boy scout rule. If you do the work in this PR you can always split the refactoring to a separate PR before it's merged.

@LikithaVemulapalli what do you think?

[LikithaVemulapalli]

Yes I agree with @stevehipwell here, let's separate refactoring PR to have a clear idea on the changes made. @phuhung273 if you want to test your changes for this PR let me know I will approve and run so for the future commits you can verify if the existing tests are working, if there are any conflicts or not, once you change the PR status to ready I will run the workflow, appreciate for your contribution. Thanks!