Replaced "true" with true in snapshot restore docs

Closes elastic#19947

Author: clintongormley

docs/reference/modules/snapshots.asciidoc

@@ -38,7 +38,7 @@ which returns:
  "my_backup": {
  "type": "fs",
  "settings": {
- "compress": "true",
+ "compress": true,
  "location": "/mount/backups/my_backup"
  }
  }
@@ -219,7 +219,7 @@ specifying the list of indices in the body of the snapshot request.
 PUT /_snapshot/my_backup/snapshot_1
 {
  "indices": "index_1,index_2",
- "ignore_unavailable": "true",
+ "ignore_unavailable": true,
  "include_global_state": false
 }
 -----------------------------------
@@ -340,7 +340,7 @@ with associated indices
 POST /_snapshot/my_backup/snapshot_1/_restore
 {
  "indices": "index_1,index_2",
- "ignore_unavailable": "true",
+ "ignore_unavailable": true,
  "include_global_state": true,
  "rename_pattern": "index_(.+)",
  "rename_replacement": "restored_index_$1"