[7.x] fix: ensure ES index names are lowercase (#4295)

[simitt]

Backports the following commits to 7.x:

• fix: ensure ES index names are lowercase (fix: ensure ES index names are lowercase #4295)

[codecov-io]

Codecov Report

Merging #4302 into 7.x will increase coverage by 4.46%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##              7.x    #4302      +/-   ##
==========================================
+ Coverage   75.79%   80.25%   +4.46%     
==========================================
  Files          64      158      +94     
  Lines        3669     8642    +4973     
==========================================
+ Hits         2781     6936    +4155     
- Misses        888     1706     +818     

Impacted Files	Coverage Δ
agentcfg/cache.go	85.71% <ø> (ø)
agentcfg/fetch.go	87.87% <ø> (ø)
agentcfg/model.go	100.00% <ø> (ø)
beater/api/asset/sourcemap/handler.go	88.00% <ø> (ø)
beater/api/config/agent/handler.go	94.95% <ø> (ø)
beater/api/expvar.go	0.00% <ø> (ø)
beater/api/intake/handler.go	97.26% <ø> (ø)
beater/api/mux.go	90.58% <ø> (ø)
beater/api/profile/handler.go	89.62% <ø> (ø)
beater/api/ratelimit/store.go	91.30% <ø> (ø)
... and 190 more

[apmmachine]

💚 Build Succeeded

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Build stats

• Build Cause: [Pull request #4302 opened]

• Start Time: 2020-10-12T08:52:28.435+0000

• Duration: 29 min 32 sec

Test stats 🧪

Test	Results
Failed	0
Passed	4038
Skipped	142
Total	4180

Steps errors

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• Name: Compress

  • Description: tar --exclude=coverage-files.tgz -czf coverage-files.tgz coverage

  • Duration: 0 min 0 sec

  • Start Time: 2020-10-12T09:08:11.154+0000

  • log

• Name: Compress

  • Description: tar --exclude=system-tests-linux-files.tgz -czf system-tests-linux-files.tgz system-tests

  • Duration: 0 min 0 sec

  • Start Time: 2020-10-12T09:20:57.854+0000

  • log