doc: add dynamodb session manager documentation

[jeromevdl]

Description

Adding documentation for a new feature (DynamoDB session manager)

Type of Change

• New content addition

Motivation and Context

This documentation goes with the newly added feature, cf PR

Areas Affected

Session management page, adding a new built-in manager (dynamoDB)

Screenshots

Checklist

• I have read the CONTRIBUTING document
• My changes follow the project's documentation style
• I have tested the documentation locally using mkdocs serve
• [] Links in the documentation are valid and working ==> I cannot update the api-reference as the library is not updated/available.
• Images/diagrams are properly sized and formatted
• All new and existing tests pass

Additional Notes

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.