Fixed xContent dependencies due to OSCore changes

[Angie-Zhang]

Issue #, if available:

opensearch-project/OpenSearch#6841

Description of changes:

1. Bump version of 2.x to 2.7;
2. Update gradle.build;
3. Fix xContent dependencies change.

CheckList:

• Commits are signed per the DCO using --signoff

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

Security test workflows fail as security plugin has not been updated yet.

[codecov-commenter]

Codecov Report

Merging #721 (205f2b4) into 2.x (1e278d0) will increase coverage by 0.45%.
The diff coverage is 60.00%.

❗ Current head 205f2b4 differs from pull request most recent head 532869a. Consider uploading reports for the commit 532869a to get more accurate results

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@@             Coverage Diff              @@
##                2.x     #721      +/-   ##
============================================
+ Coverage     75.27%   75.73%   +0.45%     
- Complexity     2636     2660      +24     
============================================
  Files           333      333              
  Lines         15398    15398              
  Branches       2386     2388       +2     
============================================
+ Hits          11591    11661      +70     
+ Misses         2435     2377      -58     
+ Partials       1372     1360      -12     

Impacted Files	Coverage Δ
...pensearch/indexmanagement/IndexManagementPlugin.kt	90.07% <ø> (ø)
...management/common/model/dimension/DateHistogram.kt	78.02% <ø> (ø)
...ndexmanagement/common/model/dimension/Dimension.kt	95.23% <ø> (ø)
...ndexmanagement/common/model/dimension/Histogram.kt	69.56% <ø> (ø)
...ch/indexmanagement/common/model/dimension/Terms.kt	77.77% <ø> (ø)
...dexmanagement/common/model/notification/Channel.kt	48.38% <ø> (ø)
...anagement/indexstatemanagement/ISMActionsParser.kt	91.80% <ø> (ø)
...ndexstatemanagement/IndexStateManagementHistory.kt	77.24% <ø> (ø)
...agement/indexstatemanagement/ManagedIndexRunner.kt	47.13% <ø> (ø)
...agement/indexstatemanagement/action/AliasAction.kt	63.63% <ø> (ø)
... and 122 more

... and 5 files with indirect coverage changes

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[Angie-Zhang]

Multi node test workflow failed for known flaky tests. Cases passed in local.

[bowenlan-amzn]

Thanks!