[Enhancement][Opensearch] - Cannot use an existing service account

[c3-davidtran]

Is your feature request related to a problem? Please describe.
When deploying Opensearch helm chart with latest 2.14.1 version, if I set rbac create to false and provide a serviceAccount name, no serviceAccount will be used by the statefulsets.

Describe the solution you'd like
I'd like to add a condition to the statefulset helm chart to support using a user provided service account that already exists.

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

Additional context
Starting 2.13.0 version, this feature has been removed.

[prudhvigodithi]

[Untriage]
Adding @tranngocsongtruc @SkollRyu @premkirank can you please take a look?