Azure snapshots can not be restored anymore

[dadoonet]

While working on #26751 and doing some manual integration testing I found that this #22858 removed an important line of our code:

AzureRepository overrides default initializeSnapshot method which creates metadata files and do other stuff.

But with PR #22858, I wrote:

    @Override
    public void initializeSnapshot(SnapshotId snapshotId, List<IndexId> indices, MetaData clusterMetadata) {
        if (blobStore.doesContainerExist(blobStore.container()) == false) {
            throw new IllegalArgumentException("The bucket [" + blobStore.container() + "] does not exist. Please create it before " +
                " creating an azure snapshot repository backed by it.");
        }
    }

instead of

    @Override
    public void initializeSnapshot(SnapshotId snapshotId, List<IndexId> indices, MetaData clusterMetadata) {
        if (blobStore.doesContainerExist(blobStore.container()) == false) {
            throw new IllegalArgumentException("The bucket [" + blobStore.container() + "] does not exist. Please create it before " +
                " creating an azure snapshot repository backed by it.");
        }
        super.initializeSnapshot(snapshotId, indices, clusterMetadata);
    }

As we never call super.initializeSnapshot(...) files are not created and we can't restore what we saved.

I'm marking this as a blocker for 6.0.0.
I'm going to send a PR anytime soon.