Increase timeout for GetAllLFSPointers RPC call

What does this MR do?

Applying this commit will use long_timeout for get_all_lfs_pointers gitaly GRPC.

Currently, get_all_lfs_pointers 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 "succeed" without having actually fetched any objects or packed-refs, presumably because fetching the lfs pointers for larger projects may take longer than 30 seconds.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
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• Style guides
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• 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

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• 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
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