Docs: redirect old Maven Repo docs to new ones

doc/administration/maven_packages.md

+This document was moved to [another location](maven_repository.md).

doc/administration/maven_repository.md

-# GitLab Maven Repository administration
+# GitLab Maven Repository administration **[PREMIUM ONLY]**
 
 >
 [Introduced](https://gitlab.com/gitlab-org/gitlab-ee/issues/5811)

doc/user/project/index.md

@@ -86,7 +86,7 @@ website with GitLab Pages
 - [Syntax highlighting](highlighting.md): An alternative to customize
 your code blocks, overriding GitLab's default choice of language
 - [Badges](badges.md): Badges for the project overview
-- [Maven packages](packages/maven.md): Your private Maven repository in GitLab **[PREMIUM]**
+- [Maven packages](packages/maven_repository.md): Your private Maven repository in GitLab **[PREMIUM]**
 - [Code owners](code_owners.md): Specify code owners for certain files **[STARTER]**
 
 ### Project's integrations

doc/user/project/packages/maven.md

+This document was moved to [another location](maven_repository.md).

doc/user/project/packages/maven_packages.md

+This document was moved to [another location](maven_repository.md).