Changing the name of osd plugin-helpers file naming to match the config

[Tengda-He]

Is your feature request related to a problem? Please describe.
The opensearch-dashboards-plugin-helpers.dev.json file in gantt-chart should be named .opensearch_dashboards-plugin-helpers.json according to https://github.com/opensearch-project/OpenSearch-Dashboards/tree/9a2d3e6918760c4bba8b44b9e8dfcd14e459a916/packages/osd-plugin-helpers#configuration

Describe the solution you'd like
Changing the name of plugin-helpers file naming to match the config as mentioned here. The previous file name is "opensearch-dashboards-plugin-helpers.dev.json", shoudl change to".opensearch_dashboards-plugin-helpers.json"

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.