updating link-record endpoint to use either schema

[ericbuckley]

Description

Making changes to main.py link-record route so the user can opt to use either of the two schemas, and the code required to interact with them, via a request header. Also adding OpenTelemetry so we can trace the linking algorithm and its performance.

Related Issues

closes #24

Additional Notes

• The X-Use-Simple-Link request header can be sent with a true value to indicate the new schema should be used.
• added src/recordlinker/database.py and moved session creation code there.
• updated the get_block_data function to use the new sqlalchemey querying syntax and resolved an issue where the query could return duplicate rows

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• The tests cover the new changes and pass successfully.
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[cbrinson-rise8]

Looks good!