add migration steps to SCIM docs (#23624)

## Description
- Adds missing migration steps to SCIM docs
- Ignore vale, I am not referencing Docker Team as in the subscription

## Preview

https://deploy-preview-23624--docsdocker.netlify.app/enterprise/security/provisioning/scim/#migrate-existing-jit-users-to-scim

## Related issues or tickets
https://docker.atlassian.net/browse/ENGDOCS-3084

## Reviews
@madisonsilva thank you again for the feedback! I have added the first
set of docs you sent to us, steps for SCIM migration

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Co-authored-by: Craig Osterhout <[email protected]>

Author: sarahsanders-docker