Upgrades supported ES version to 7.10

[dbbaughe]

Issue #, if available:

Description of changes:

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

Merging #349 (5e52d3a) into master (f62beef) will increase coverage by 0.57%.
The diff coverage is 96.07%.

@@             Coverage Diff              @@
##             master     #349      +/-   ##
============================================
+ Coverage     75.06%   75.63%   +0.57%     
- Complexity     1358     1374      +16     
============================================
  Files           183      183              
  Lines          7011     7011              
  Branches       1143     1143              
============================================
+ Hits           5263     5303      +40     
+ Misses         1135     1097      -38     
+ Partials        613      611       -2     

Impacted Files	Coverage Δ	Complexity Δ
...nt/indexstatemanagement/ManagedIndexCoordinator.kt	61.90% <ø> (+0.41%)	35.00 <0.00> (ø)
...agement/indexstatemanagement/ManagedIndexRunner.kt	55.04% <0.00%> (ø)	41.00 <0.00> (ø)
...nt/indexstatemanagement/model/ErrorNotification.kt	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
...ticsearch/indexmanagement/IndexManagementPlugin.kt	92.10% <100.00%> (ø)	11.00 <0.00> (ø)
...ch/indexmanagement/elasticapi/ElasticExtensions.kt	80.00% <100.00%> (ø)	0.00 <0.00> (ø)
...ndexstatemanagement/IndexStateManagementHistory.kt	76.19% <100.00%> (+0.22%)	26.00 <0.00> (-1.00)	⬆️
...agement/indexstatemanagement/model/ChangePolicy.kt	90.47% <100.00%> (ø)	8.00 <0.00> (ø)
...t/indexstatemanagement/model/ManagedIndexConfig.kt	78.57% <100.00%> (+2.04%)	20.00 <0.00> (+2.00)
...indexstatemanagement/model/ManagedIndexMetaData.kt	89.44% <100.00%> (+3.72%)	41.00 <0.00> (+1.00)
...dexmanagement/indexstatemanagement/model/Policy.kt	90.36% <100.00%> (+1.20%)	22.00 <0.00> (+1.00)
... and 56 more

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