Docs: Update plugins.asciidoc on river plugins section

Adding links to Amazon S3 and Google Drive river plugins

Closes #8544

docs/reference/modules/plugins.asciidoc

@@ -251,6 +251,8 @@ You can disable that check using `plugins.check_lucene: false`.
 * https://github.com/salyh/elasticsearch-river-imap[IMAP/POP3 Email River Plugin] (by Hendrik Saly)
 * https://github.com/codelibs/elasticsearch-river-web[Web River Plugin] (by CodeLibs Project)
 * https://github.com/eea/eea.elasticsearch.river.rdf[EEA ElasticSearch RDF River Plugin] (by the European Environment Agency)
+* https://github.com/lbroudoux/es-amazon-s3-river[Amazon S3 River Plugin] (by Laurent Broudoux)
+* https://github.com/lbroudoux/es-google-drive-river[Google Drive River Plugin] (by Laurent Broudoux)
 
 [float]
 [[transport]]