Index Encounters using OpenSearch

[TanyaStere42]

Feature description and context

• Develop an OpenSearch class to provide general OpenSearch functionality to Wildbook: index creation, indexing (foreground, background), searching (via method and via api), etc.
• Implement above on Encounter.java using the new base class (#509)

Feature sign-off requirements

• Encounters can be indexed in OpenSearch:
  • manually via a method on an encounter
  • background/foreground index of entire class
  • OpenSearch documents verified on servers
• Encounters can be searched:
  • via method on class
  • via api (should respect "security")

Testing considerations

• Regardless of method of integration with permissions structure, must accurately restrict encounter visibility based on encounter ownership/user role/organization/project membership/collaboration status

Architectural Design Notes

• Utilizes OpenSearch server(s) as established via #510 (will required opensearch.properties or similar)