Change log level to INFO for messages about alpha plugin versions (#2693)

(cherry picked from commit 8317436)

Author: IgnatBeresnev

plugins/gfm/src/main/kotlin/org/jetbrains/dokka/gfm/GfmPlugin.kt

@@ -43,7 +43,7 @@ class GfmPlugin : DokkaPlugin() {
     internal val alphaVersionNotifier by extending {
         CoreExtensions.postActions providing { ctx ->
             PostAction {
-                ctx.logger.warn("GFM output format is in Alpha version, use at your own risk, expect bugs and migration issues")
+                ctx.logger.info("GFM output format is in Alpha version, use at your own risk, expect bugs and migration issues")
             }
         }
     }

plugins/javadoc/src/main/kotlin/org/jetbrains/dokka/javadoc/JavadocPlugin.kt

@@ -86,7 +86,7 @@ class JavadocPlugin : DokkaPlugin() {
     internal val alphaVersionNotifier by extending {
         CoreExtensions.postActions providing { ctx ->
             PostAction {
-                ctx.logger.warn("Javadoc output format is in Alpha version, use at your own risk, expect bugs and migration issues")
+                ctx.logger.info("Javadoc output format is in Alpha version, use at your own risk, expect bugs and migration issues")
             }
         }
     }

plugins/jekyll/src/main/kotlin/JekyllPlugin.kt

@@ -52,7 +52,7 @@ class JekyllPlugin : DokkaPlugin() {
     internal val alphaVersionNotifier by extending {
         CoreExtensions.postActions providing { ctx ->
             PostAction {
-                ctx.logger.warn("Jekyll output format is in Alpha version, use at your own risk, expect bugs and migration issues")
+                ctx.logger.info("Jekyll output format is in Alpha version, use at your own risk, expect bugs and migration issues")
             }
         }
     }

plugins/kotlin-as-java/src/main/kotlin/KotlinAsJavaPlugin.kt

@@ -34,7 +34,7 @@ class KotlinAsJavaPlugin : DokkaPlugin() {
     internal val alphaVersionNotifier by extending {
         CoreExtensions.postActions providing { ctx ->
             PostAction {
-                ctx.logger.warn("KotlinAsJava plugin is in Alpha version, use at your own risk, expect bugs and migration issues")
+                ctx.logger.info("KotlinAsJava plugin is in Alpha version, use at your own risk, expect bugs and migration issues")
             }
         }
     }