Geo: Fix undefined method 'log_error' in BlobDownloader

What does this MR do and why?

Gitlab::Geo::Replication::BlobDownloader was calling log_error but only included EE::GeoHelper, which does not define that method. This adds ::Gitlab::Geo::LogHelpers to BlobDownloader so that directory creation failures are logged correctly instead of raising a NoMethodError that masks the real sync error.

References

#598565 (closed)

How to set up and validate locally

Before the change:

• patch Gitlab::Geo::Replication::BlobDownloader with a new method:

def test_log
  log_error('oops')
end

• In the Rails console, run:

replicator = Project.first.replicator
bd = Gitlab::Geo::Replication::BlobDownloader.new(replicator:)
bd.test_log

• See it raise a NoMethodError exception
• Stash the patch

After the change:

• Checkout the branch.
• Un-stash the patch, restart the Rails console and repeat the steps.
• Now db.test_log should return true, as asserted by the new spec added.

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