7.15.1 version bump (#2243)

Bumps version for the 7.15.0 release

DO NOT MERGE UNTIL RELEASE DAY

Author: KOTungseth

shared/versions/stack/7.15.asciidoc

@@ -1,12 +1,12 @@
-:version:                7.15.0
+:version:                7.15.1
 ////
 bare_version never includes -alpha or -beta
 ////
-:bare_version:           7.15.0
-:logstash_version:       7.15.0
-:elasticsearch_version:  7.15.0
-:kibana_version:         7.15.0
-:apm_server_version:     7.15.0
+:bare_version:           7.15.1
+:logstash_version:       7.15.1
+:elasticsearch_version:  7.15.1
+:kibana_version:         7.15.1
+:apm_server_version:     7.15.1
 :branch:                 7.15
 :minor-version:          7.15
 :major-version:          7.x