implementing a session creation mutation in GraphQL

### Context

The issue involves implementing a session creation mutation in GraphQL. Currently, this functionality is only available through REST.

### Acceptance criteria

- Implement the session creation mutation in GraphQL.
- Ensure that the new mutation provides the same functionality as the existing REST method.

### Other information

- Important mutation currently only available via REST.
- [Link to the message](https://teams.microsoft.com/l/message/19:14c484402d874dafb15806d093b95a82@thread.skype/1770948250554?tenantId=13c6a44d-9b52-4b9e-aa34-0513ee7131f2&groupId=74ae2c4d-ec4d-4fdf-b2c2-f5041d1e8631&parentMessageId=1770947557748&teamName=devops&channelName=Frontend&createdTime=1770948250554)

JIRA Issue: BA-4496

No repository files or tests are named. Start by locating the existing REST session-creation method and the GraphQL mutation entry points, then compare their inputs and behavior; done means the GraphQL mutation provides the same functionality as REST.

Written by the indexing model from the issue text.