Add extra volumes to migrate job

[Zach-Johnson]

This PR adds the extraVolumes and extraVolumeMounts to the migration job.

Description

I have a use case where I want to mount a CA cert bundle into the openfga deployment which is used
for the database connection.
It works fine for service, but the migration has no way that I can see to get the cert currently.
I think it is probably okay to re-use the existing vars for the volumes in the migrate job,
but I'm happy to move those to a separate value if that is preferable.

References

Review Checklist

• I have clicked on "allow edits by maintainers".
• I have added documentation for new/changed functionality in this PR or in a PR to openfga.dev [Provide a link to any relevant PRs in the references section above]
• The correct base branch is being used, if not main
• I have added tests to validate that the change in functionality is working as expected

[Zach-Johnson]

Hey, any way to get a review on this?