### 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
leaderClient().admin()
                .indices()
                .prepareCreate("index1")
                .setSettings(
                    Settings.builder()
                        .put(IndexMetadata.SETTING_NUMBER_OF_SHARDS, 1)
                        .put(IndexMetadata.SETTING_NUMBER_OF_REPLICAS, 0)
                        .build()
                )
        );
        final PutFollowAction.Request followRequest = putFollow("index1", "index2");
        followerClient().execute(PutFollowAction.INSTANCE, followRequest).get();
        leaderClient().prepareIndex("index1").setId("1").setSource("{}", XContentType.JSON).get();
        assertBusy(() -> assertThat(followerClient().prepareSearch("index2").get().getHits().getTotalHits().value, equalTo(1L)));
        leaderClient().admin().indices().delete(new DeleteIndexRequest("index1")).actionGet();
        assertBusy(() -> {
            StatsResponses response = followerClient().execute(FollowStatsAction.INSTANCE, new StatsRequest()).actionGet();
            assertThat(response.getNodeFailures(), empty());
            assertThat(response.getTaskFailures(), empty());
            assertThat(response.getStatsResponses(), hasSize(1));
            assertThat(response.getStatsResponses().get(0).status().failedReadRequests(), greaterThanOrEqualTo(1L));
            ElasticsearchException fatalException = response.getStatsResponses().get(0).status().getFatalException();
            assertThat(fatalException, notNullValue());
            assertThat(fatalException.getRootCause().getMessage(), equalTo("no such index [index1]"));
        });
        pauseFollow("index2");
        ensureNoCcrTasks();
    }
    public void testFollowClosedIndex() {
        final String leaderIndex = "test-index";