Use long_timeout for fetch_internal_remote GRPC

What does this MR do?

Applying this commit will use long_timeout for fetch_internal_remote gitaly GRPC.

Currently, fetch_internal_remote uses GitalyClient.medium_timeout which is set to 30 seconds in the GitLab.com application admin settings.

At a high level, this is causing project migrations of larger projects to fail, presumably because fetching the refs for larger projects may take longer than 30 seconds.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team