Refactor java migration guides (#7315)

* Refactor migration guide for Java SDK (split in different pages; create better overview of available migration guides on index page
* Change sidebar order to reflect order of other SDKs

Author: stephanie-anderson

src/platforms/java/common/configuration/index.mdx

@@ -1,6 +1,6 @@
 ---
 title: Configuration
-sidebar_order: 10
+sidebar_order: 5
 description: "Learn more about how to configure the SDK. These options are set when the SDK is first initialized, passed to the init method as an object."
 ---
 

src/platforms/java/common/legacy/usage.mdx

@@ -1,5 +1,5 @@
 ---
-title: Manual Usage
+title: Usage
 sidebar_order: 15
 redirect_from:
   - /clients/java/usage/

src/platforms/java/common/scope.mdx

@@ -1,6 +1,6 @@
 ---
 title: Scope & Breadcrumbs
-sidebar_order: 3
+sidebar_order: 11
 redirect_from:
   - /clients/java/context/
 ---