Commit with the committer's timezone in UserApplyPatch

UserApplyPatch always commits the patches with the time zone set to +0000. Other RPCs commit with the user's timezone. We should fix this in the RPC once the feature flag has been removed.

The following discussion from !3066 (merged) should be addressed:

@pks-t started a discussion: (+2 comments)

	committerTime, err := dateFromProto(header)
	if err != nil {
		return fmt.Errorf("committer time: %w", err)
	}

This'll also take the user's timezone into account.

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