[fix][function] Fix invalid metric type "gauge "

[coderzc]

Motivation

Prometheus load metrics error.

curl -s 'http://localhost:8080/metrics/'

This bug introduce from #15558

Modifications

Remove the space behind the metric type.

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

Matching PR in forked repository

PR in forked repository:

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 46.58%. Comparing base (6c65ca0) to head (55dbe86).
⚠️ Report is 3532 commits behind head on master.

Files with missing lines	Patch %	Lines
...he/pulsar/functions/worker/WorkerStatsManager.java	0.00%	2 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             master   #18129       +/-   ##
=============================================
+ Coverage     34.91%   46.58%   +11.66%     
- Complexity     5707    17884    +12177     
=============================================
  Files           607     1574      +967     
  Lines         53396   128474    +75078     
  Branches       5712    14134     +8422     
=============================================
+ Hits          18644    59848    +41204     
- Misses        32119    62426    +30307     
- Partials       2633     6200     +3567     

Flag	Coverage Δ
unittests	46.58% <0.00%> (+11.66%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...he/pulsar/functions/worker/WorkerStatsManager.java	1.14% <0.00%> (ø)

... and 1151 files with indirect coverage changes

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[coderzc]

@Technoboy- Also need to cherry-pick 2.9.x.

[asafm]

Oh, man. Who would have thought this would be an issue? We probably need an e2e test using real Prometheus docker on this. Thanks for the fix @coderzc .

@marksilcox CC