Add 7.0 -> 8.0 Migration Guide

Closes gh-17182

Author: jzheaux

docs/modules/ROOT/nav.adoc

@@ -2,14 +2,11 @@
 * xref:prerequisites.adoc[Prerequisites]
 * xref:community.adoc[Community]
 * xref:whats-new.adoc[What's New]
-* xref:migration-7/index.adoc[Preparing for 7.0]
-** xref:migration-7/authentication.adoc[Authentication]
-** xref:migration-7/authorization.adoc[Authorization]
-** xref:migration-7/configuration.adoc[Configuration]
-** xref:migration-7/ldap.adoc[LDAP]
-** xref:migration-7/oauth2.adoc[OAuth 2.0]
-** xref:migration-7/web.adoc[Web]
-* xref:migration/index.adoc[Migrating to 6]
+* xref:migration-8/index.adoc[Preparing for 8.0]
+* xref:migration/index.adoc[Migrating to 7]
+** xref:migration/servlet/index.adoc[Servlet]
+*** xref:migration/servlet/oauth2.adoc[OAuth 2.0]
+** xref:migration/reactive.adoc[Reactive]
 * xref:getting-spring-security.adoc[Getting Spring Security]
 * xref:attachment$api/java/index.html[Javadoc]
 * xref:features/index.adoc[Features]