feat: Support for pending count with Adaptive lookback

[RohanAshar]

Continuation of #2373

This adds the pending calculation in the daemon and emits the metric. Timeline is now maintained in the daemon. Currently uses the 1m value of pending metric. This will change once we have the monovertex starts sending the lag metric without the timeline calculation.

Follow Up Work:

• Monovertex to send pending lag without the timeline calculation to daemon
• Monovertex to call pending for only pod 0

[kohlisid]

#2487
PR for the lag reader changes! Adds the new impl but triggers it only for monovertex right now.
Once similar changes are made for pipeline, then we can switch both monovertex and pipeline to the new impl.
Requires clean up!
We can discuss if we want to break this down in parts and merge, or only merge when both are done!

[codecov]

Codecov Report

Attention: Patch coverage is 60.81081% with 29 lines in your changes missing coverage. Please review.

Project coverage is 70.01%. Comparing base (3c04495) to head (09844bc).

Files with missing lines	Patch %	Lines
pkg/mvtxdaemon/server/service/rater/rater.go	47.91%	18 Missing and 7 partials ⚠️
pkg/mvtxdaemon/server/service/rater/helper.go	87.50%	2 Missing and 1 partial ⚠️
pkg/mvtxdaemon/server/service/mvtx_service.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2486      +/-   ##
==========================================
- Coverage   70.10%   70.01%   -0.10%     
==========================================
  Files         391      391              
  Lines       58243    58268      +25     
==========================================
- Hits        40834    40799      -35     
- Misses      16310    16363      +53     
- Partials     1099     1106       +7     

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