[github & gitlab] IJPL-171311 Bundle ultimate plugin versions into community IDEs built by ourselves

The existing gitlab.community and github.community modules that describe community versions of plugins with less functionality included do still exist intentionally. This is required for external developers to be able to build IDE from community project sources and get both plugins working there out of the box. Thus community plugins are still listed in IdeaCommunityProperties and PyCharmCommunityProperties. This part is only required for third-party folks. As for internal builds, they employ a build context produced by `org.jetbrains.intellij.build.IdeaUltimateBuilderKt.createBuildContextForCommunityProduct` which in turn prefers github.ultimate and gitlab.ultimate plugin distributions over community ones

GitOrigin-RevId: e8233c7133d63abe3aefa684cc57ed9bad9fee64

plugins/github/community/resources/META-INF/plugin.xml

@@ -1,5 +1,4 @@
-<idea-plugin package="org.jetbrains.plugins.github" xmlns:xi="http://www.w3.org/2001/XInclude"
-             allow-bundled-update="true">
+<idea-plugin package="org.jetbrains.plugins.github" allow-bundled-update="false">
   <name>GitHub</name>
   <id>org.jetbrains.plugins.github</id>
   <vendor>JetBrains</vendor>

plugins/gitlab/gitlab-community/resources/META-INF/plugin.xml

@@ -1,5 +1,4 @@
-<idea-plugin package="org.jetbrains.plugins.gitlab.community"
-             allow-bundled-update="true">
+<idea-plugin package="org.jetbrains.plugins.gitlab.community" allow-bundled-update="false">
 
   <!-- Warn: remember to sync the following {name, id, vendor, category, description} tags
              with plugin.xml in intellij.vcs.gitlab.ultimate module-->