[7.x] aggregation/txmetrics: don't group on user-agent (#3848)

[axw]

Backports the following commits to 7.x:

• aggregation/txmetrics: don't group on user-agent (aggregation/txmetrics: don't group on user-agent #3848)

[codecov-commenter]

Codecov Report

Merging #3854 into 7.x will increase coverage by 0.07%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##              7.x    #3854      +/-   ##
==========================================
+ Coverage   79.82%   79.89%   +0.07%     
==========================================
  Files         137      137              
  Lines        6166     6163       -3     
==========================================
+ Hits         4922     4924       +2     
+ Misses       1244     1239       -5     

Impacted Files	Coverage Δ
...ack/apm-server/aggregation/txmetrics/aggregator.go	93.22% <ø> (-0.11%)	⬇️
kibana/connecting_client.go	72.58% <0.00%> (+8.06%)	⬆️

[apmmachine]

💚 Build Succeeded

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Build stats

• Build Cause: [Pull request #3854 opened]

• Start Time: 2020-06-08T06:39:38.879+0000

• Duration: 27 min 43 sec

Test stats 🧪

Test	Results
Failed	0
Passed	3017
Skipped	142
Total	3159

Steps errors

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• Name: Test Sync

  • Description: ./script/jenkins/sync.sh

  • Duration: 3 min 56 sec

  • Start Time: 2020-06-08T06:50:33.324+0000

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