Added a simple, single document RFS ES 6.8 Jenkins Integ Test

[chelma]

Description

Added a simple integ test exercising the user workflow for RFS from an ES 6.8 source.

Issues Resolved

• https://opensearch.atlassian.net/browse/MIGRATIONS-1956

Testing

• Here's an Jenkins run demonstrating the new Pipeline
  • https://migrations.ci.opensearch.org/job/rfs-es68source-e2e-test/14/console

Check List

• New functionality includes testing
  • All tests pass, including unit test, integration test and doctest
• New functionality has been documented
• Commits are signed per the DCO using --signoff

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.16%. Comparing base (18d55fb) to head (ad77aad).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #1062   +/-   ##
=========================================
  Coverage     80.16%   80.16%           
  Complexity     2744     2744           
=========================================
  Files           367      367           
  Lines         13743    13743           
  Branches        949      949           
=========================================
  Hits          11017    11017           
  Misses         2149     2149           
  Partials        577      577           

Flag	Coverage Δ
gradle-test	78.07% <ø> (ø)
python-test	90.24% <ø> (ø)

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