[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

Merging #18129 (55dbe86) into master (6c65ca0) will increase coverage by 16.85%.
The diff coverage is 68.96%.

@@              Coverage Diff              @@
##             master   #18129       +/-   ##
=============================================
+ Coverage     34.91%   51.77%   +16.85%     
- Complexity     5707     7251     +1544     
=============================================
  Files           607      393      -214     
  Lines         53396    43484     -9912     
  Branches       5712     4471     -1241     
=============================================
+ Hits          18644    22514     +3870     
+ Misses        32119    18458    -13661     
+ Partials       2633     2512      -121     

Flag	Coverage Δ
unittests	51.77% <68.96%> (+16.85%)	⬆️

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

Impacted Files	Coverage Δ
...pache/pulsar/broker/admin/impl/NamespacesBase.java	63.98% <ø> (+49.45%)	⬆️
.../pulsar/broker/service/AbstractBaseDispatcher.java	50.30% <ø> (+4.44%)	⬆️
...che/pulsar/broker/service/BacklogQuotaManager.java	12.39% <0.00%> (+2.91%)	⬆️
.../service/SystemTopicBasedTopicPoliciesService.java	62.97% <0.00%> (+11.38%)	⬆️
.../pulsar/broker/stats/BrokerOperabilityMetrics.java	100.00% <ø> (+7.35%)	⬆️
...g/apache/pulsar/compaction/CompactedTopicImpl.java	69.28% <0.00%> (+58.57%)	⬆️
.../org/apache/pulsar/broker/admin/v2/Namespaces.java	57.36% <50.00%> (+49.33%)	⬆️
...ache/pulsar/broker/service/EntryFilterSupport.java	32.43% <50.00%> (+7.43%)	⬆️
...apache/pulsar/proxy/server/DirectProxyHandler.java	63.63% <50.00%> (ø)
...broker/delayed/InMemoryDelayedDeliveryTracker.java	65.00% <75.00%> (+65.00%)	⬆️
... and 406 more

[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