### 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
if (response.getStatsResponses().isEmpty() == false) {
                assertThat(response.getStatsResponses(), hasSize(1));
                assertThat(response.getStatsResponses().get(0).status().failedWriteRequests(), greaterThanOrEqualTo(1L));
                ElasticsearchException fatalException = response.getStatsResponses().get(0).status().getFatalException();
                assertThat(fatalException, notNullValue());
                assertThat(fatalException.getMessage(), equalTo("no such index [index2]"));
            }
        });
        ensureNoCcrTasks();
    }
    public void testPauseIndex() throws Exception {
        assertAcked(
            leaderClient().admin()
                .indices()
                .prepareCreate("leader")
                .setSettings(
                    Settings.builder()
                        .put(IndexMetadata.SETTING_NUMBER_OF_SHARDS, 1)
                        .put(IndexMetadata.SETTING_NUMBER_OF_REPLICAS, 0)
                        .build()
                )
        );
        followerClient().execute(PutFollowAction.INSTANCE, putFollow("leader", "follower")).get();
        assertAcked(followerClient().admin().indices().prepareCreate("regular-index").setMasterNodeTimeout(TimeValue.MAX_VALUE));
        assertAcked(followerClient().execute(PauseFollowAction.INSTANCE, new PauseFollowAction.Request("follower")).actionGet());
        assertThat(
            expectThrows(
                IllegalArgumentException.class,
                () -> followerClient().execute(PauseFollowAction.INSTANCE, new PauseFollowAction.Request("follower")).actionGet()
            ).getMessage(),