### Description

It is impossible to create a follower index with a `$` character in its name (please note, it is possible to create a regular index with `$` in its name).

This could be reproduced by rest request:
```
PUT /my-index/_ccr/follow
{
    "remote_cluster": "my-remote-cluster",
    "leader_index": "my-index$follower"
}
```

or `CcrIntegTestCase`:

```
    public void testFollowIndex() throws Exception {
        assertAcked(leaderClient().admin().indices().prepareCreate("my$index"));
        setupRemoteCluster();
        final PutFollowAction.Request followRequest = putFollow("my$index", "my$index");
        followerClient().execute(PutFollowAction.INSTANCE, followRequest).get();
    }
```

This is happening as during initial follow phase we restore the leader cluster from the remote using a snapshot restore.
Corresponding request is created with index name added to `RestoreSnapshotRequest#renamePattern` (regexp) without escaping `$`.

x-pack/plugin/ccr/src/internalClusterTest/java/org/elasticsearch/xpack/ccr/IndexFollowingIT.java
assertBusy(() -> {
            
            GetSettingsRequest getSettingsRequest = new GetSettingsRequest();
            getSettingsRequest.indices("follower");
            GetSettingsResponse getSettingsResponse = followerClient().admin().indices().getSettings(getSettingsRequest).actionGet();
            assertThat(getSettingsResponse.getSetting("follower", "index.max_ngram_diff"), equalTo("2"));
            assertThat(getFollowTaskSettingsVersion("follower"), equalTo(2L));
            try {
                assertThat(
                    followerClient().prepareSearch("follower").get().getHits().getTotalHits().value,
                    equalTo(firstBatchNumDocs + secondBatchNumDocs)
                );
            } catch (Exception e) {
                throw new AssertionError("error while searching", e);
            }
        });
        assertThat(hasFollowIndexBeenClosedChecker.getAsBoolean(), is(false));
    }
    public void testLeaderIndexSettingNotPercolatedToFollower() throws Exception {
        
        
        
        final String leaderIndexSettings = getIndexSettings(1, 0);
        assertAcked(leaderClient().admin().indices().prepareCreate("leader").setSource(leaderIndexSettings, XContentType.JSON));
        ensureLeaderYellow("leader");
        final PutFollowAction.Request followRequest = putFollow("leader", "follower");
        followerClient().execute(PutFollowAction.INSTANCE, followRequest).get();
        BooleanSupplier hasFollowIndexBeenClosedChecker = hasFollowIndexBeenClosed("follower");
        final long firstBatchNumDocs = randomIntBetween(2, 64);
        for (long i = 0; i < firstBatchNumDocs; i++) {