Renamed plugin helper config file to consistent name with OSD

[chloe-zh]

Description

The previous name of the plugin helper config file is .opensearch-dashboards-plugin-helpers.json, which is not consistent with the osd configuration, it might cause the missing of workbench build config. This pull request is to change the name to .opensearch_dashboards-plugin-helpers.json for consistency.

Issues Resolved

#227

Check List

• New functionality includes testing.
  • All tests pass, including unit test, integration test and doctest
• New functionality has been documented.
  • New functionality has javadoc added
  • New functionality has user manual doc added
• 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.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[Tengda-He]

LGTM

[Tengda-He]

LGTM

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.90%. Comparing base (efd2f4a) to head (cb113a6).
Report is 859 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #228   +/-   ##
=========================================
  Coverage     99.90%   99.90%           
  Complexity     2560     2560           
=========================================
  Files           248      248           
  Lines          6005     6005           
  Branches        346      346           
=========================================
  Hits           5999     5999           
  Misses            5        5           
  Partials          1        1           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.