[DOCS] organize a bit the repository plugins

(cherry picked from commit 88e1c20)

Author: costin

docs/reference/modules/plugins.asciidoc

@@ -168,6 +168,15 @@ bin/plugin --install mobz/elasticsearch-head --timeout 0
 * https://github.com/medcl/elasticsearch-analysis-pinyin[Pinyin Analysis Plugin] (by Medcl)
 * https://github.com/medcl/elasticsearch-analysis-string2int[String2Integer Analysis Plugin] (by Medcl)
 
+[float]
+[[discovery-plugins]]
+==== Discovery Plugins
+
+.Supported by Elasticsearch
+* https://github.com/elasticsearch/elasticsearch-cloud-aws[AWS Cloud Plugin] - EC2 discovery and S3 Repository
+* https://github.com/elasticsearch/elasticsearch-cloud-azure[Azure Cloud Plugin] - Azure discovery
+* https://github.com/elasticsearch/elasticsearch-cloud-gce[Google Compute Engine Cloud Plugin] - GCE discovery
+
 [float]
 [[river]]
 ==== River Plugins
@@ -236,16 +245,21 @@ bin/plugin --install mobz/elasticsearch-head --timeout 0
 * https://github.com/karmi/elasticsearch-paramedic[Paramedic Plugin] (by Karel Minařík)
 * https://github.com/polyfractal/elasticsearch-segmentspy[SegmentSpy Plugin] (by Zachary Tong)
 
+[float]
+[[repository-plugins]]
+==== Snapshot/Restore Repository Plugins
+
+.Supported by Elasticsearch
+
+* https://github.com/elasticsearch/elasticsearch-hadoop/tree/master/repository-hdfs[Hadoop HDFS] Repository
+* https://github.com/elasticsearch/elasticsearch-cloud-aws#s3-repository[AWS S3] Repository
+
 [float]
 [[misc]]
 ==== Misc Plugins
 
 .Supported by Elasticsearch
 * https://github.com/elasticsearch/elasticsearch-mapper-attachments[Mapper Attachments Type plugin]
-* https://github.com/elasticsearch/elasticsearch-hadoop/tree/master/repository-hdfs[Hadoop HDFS Snapshot/Restore Plugin]
-* https://github.com/elasticsearch/elasticsearch-cloud-aws[AWS Cloud Plugin] - EC2 discovery and S3 Repository
-* https://github.com/elasticsearch/elasticsearch-cloud-azure[Azure Cloud Plugin] - Azure discovery
-* https://github.com/elasticsearch/elasticsearch-cloud-gce[Google Compute Engine Cloud Plugin] - GCE discovery
 
 .Supported by the community
 * https://github.com/carrot2/elasticsearch-carrot2[carrot2 Plugin]: Results clustering with carrot2 (by Dawid Weiss)

docs/reference/modules/snapshots.asciidoc

@@ -91,7 +91,7 @@ point to the root of the shared filesystem repository. The following settings ar
 Other repository backends are available in these official plugins:
 
 * https://github.com/elasticsearch/elasticsearch-cloud-aws#s3-repository[AWS Cloud Plugin] for S3 repositories
-* https://github.com/elasticsearch/elasticsearch-hdfs[HDFS Plugin]
+* https://github.com/elasticsearch/elasticsearch-hadoop/tree/master/repository-hdfs[HDFS Plugin] for Hadoop environments
 
 [float]
 === Snapshot