Create shared helper module to make elasticsearch/ opensearch code easier to maintain

[jonhealy1]

The current implementation of the stac-fastapi-elasticsearch-opensearch repository contains duplicated logic between the elasticsearch and opensearch modules. This duplication makes the code harder to maintain and increases the risk of inconsistencies. To address this, I propose creating a new module to consolidate shared logic specific to this repository.

The new module would house shared utilities, such as:

• Common database operations (e.g., mk_actions for bulk operations).
• Validation logic.
• Shared error handling and logging utilities.
• Index information