Use CcrRepository to init follower index (#35719)

This commit modifies the put follow index action to use a
CcrRepository when creating a follower index. It routes 
the logic through the snapshot/restore process. A 
wait_for_active_shards parameter can be used to configure
how long to wait before returning the response.

docs/reference/ccr/apis/follow/get-follow-info.asciidoc

@@ -22,7 +22,7 @@ replication options and whether the follower indices are active or paused.
 
 [source,js]
 --------------------------------------------------
-PUT /follower_index/_ccr/follow
+PUT /follower_index/_ccr/follow?wait_for_active_shards=1
 {
   "remote_cluster" : "remote_cluster",
   "leader_index" : "leader_index"

docs/reference/ccr/apis/follow/get-follow-stats.asciidoc

@@ -21,7 +21,7 @@ following tasks associated with each shard for the specified indices.
 
 [source,js]
 --------------------------------------------------
-PUT /follower_index/_ccr/follow
+PUT /follower_index/_ccr/follow?wait_for_active_shards=1
 {
   "remote_cluster" : "remote_cluster",
   "leader_index" : "leader_index"

docs/reference/ccr/apis/follow/post-pause-follow.asciidoc

@@ -24,7 +24,7 @@ following task.
 
 [source,js]
 --------------------------------------------------
-PUT /follower_index/_ccr/follow
+PUT /follower_index/_ccr/follow?wait_for_active_shards=1
 {
   "remote_cluster" : "remote_cluster",
   "leader_index" : "leader_index"

docs/reference/ccr/apis/follow/post-resume-follow.asciidoc

@@ -23,7 +23,7 @@ returns, the follower index will resume fetching operations from the leader inde
 
 [source,js]
 --------------------------------------------------
-PUT /follower_index/_ccr/follow
+PUT /follower_index/_ccr/follow?wait_for_active_shards=1
 {
   "remote_cluster" : "remote_cluster",
   "leader_index" : "leader_index"

docs/reference/ccr/apis/follow/post-unfollow.asciidoc

@@ -27,7 +27,7 @@ irreversible operation.
 
 [source,js]
 --------------------------------------------------
-PUT /follower_index/_ccr/follow
+PUT /follower_index/_ccr/follow?wait_for_active_shards=1
 {
   "remote_cluster" : "remote_cluster",
   "leader_index" : "leader_index"

docs/reference/ccr/apis/follow/put-follow.asciidoc

@@ -31,7 +31,7 @@ POST /follower_index/_ccr/pause_follow
 
 [source,js]
 --------------------------------------------------
-PUT /<follower_index>/_ccr/follow
+PUT /<follower_index>/_ccr/follow?wait_for_active_shards=1
 {
   "remote_cluster" : "<remote_cluster>",
   "leader_index" : "<leader_index>"
@@ -43,6 +43,11 @@ PUT /<follower_index>/_ccr/follow
 // TEST[s/<remote_cluster>/remote_cluster/]
 // TEST[s/<leader_index>/leader_index/]
 
+The `wait_for_active_shards` parameter specifies the number of shards to wait on being active
+before responding. This defaults to waiting on none of the shards to be active. A shard must
+be restored from the leader index being active. Restoring a follower shard requires transferring
+all the remote Lucene segment files to the follower index.
+
 ==== Path Parameters
 
 `follower_index` (required)::
@@ -73,7 +78,7 @@ This example creates a follower index named `follower_index`:
 
 [source,js]
 --------------------------------------------------
-PUT /follower_index/_ccr/follow
+PUT /follower_index/_ccr/follow?wait_for_active_shards=1
 {
   "remote_cluster" : "remote_cluster",
   "leader_index" : "leader_index",

docs/reference/ccr/apis/get-ccr-stats.asciidoc

@@ -22,7 +22,7 @@ shard-level stats as in the <<ccr-get-follow-stats,get follower stats API>>.
 
 [source,js]
 --------------------------------------------------
-PUT /follower_index/_ccr/follow
+PUT /follower_index/_ccr/follow?wait_for_active_shards=1
 {
   "remote_cluster" : "remote_cluster",
   "leader_index" : "leader_index"

docs/reference/ccr/getting-started.asciidoc

@@ -230,7 +230,7 @@ cluster.
 
 [source,js]
 --------------------------------------------------
-PUT /server-metrics-copy/_ccr/follow
+PUT /server-metrics-copy/_ccr/follow?wait_for_active_shards=1
 {
   "remote_cluster" : "leader",
   "leader_index" : "server-metrics"