Extract static content from migration/index

Author: craigtaverner

docs/reference/migration/index.asciidoc

@@ -1,34 +1,4 @@
-[[breaking-changes]]
-= Migration guide
-
-This section discusses the changes that you need to be aware of to migrate
-your application to {version}. For more information about what's new in this
-release, see the <<release-highlights>> and <<es-release-notes>>.
-
-As {es} introduces new features and improves existing ones, the changes
-sometimes make older settings, APIs, and parameters obsolete. We typically
-deprecate obsolete functionality as part of a release. If possible, we support
-the deprecated functionality for several subsequent releases before removing it.
-This enables applications to continue working unchanged while you prepare to
-migrate away from the deprecated functionality.
-
-To get the most out of {es} and facilitate future upgrades, we strongly
-encourage migrating away from using deprecated functionality as soon as
-possible.
-
-To give you insight into what deprecated features you're using, {es}:
-
-- Returns a `Warn` HTTP header whenever you
-submit a request that uses deprecated functionality.
-- <<deprecation-logging, Logs deprecation warnings>> when
-deprecated functionality is used.
-- <<migration-api-deprecation, Provides a deprecation info API>>
-that scans a cluster's configuration
-and mappings for deprecated functionality.
-
-For more information about {minor-version},
-see the <<release-highlights>> and <<es-release-notes>>.
-For information about how to upgrade your cluster, see <<setup-upgrade>>.
+include::migration_intro.asciidoc[]
 
 * <<migrating-8.3,Migrating to 8.3>>
 * <<migrating-8.2,Migrating to 8.2>>
@@ -39,3 +9,4 @@ include::migrate_8_3.asciidoc[]
 include::migrate_8_2.asciidoc[]
 include::migrate_8_1.asciidoc[]
 include::migrate_8_0.asciidoc[]
+

docs/reference/migration/migration_intro.asciidoc

@@ -0,0 +1,31 @@
+[[breaking-changes]]
+= Migration guide
+
+This section discusses the changes that you need to be aware of to migrate
+your application to {version}. For more information about what's new in this
+release, see the <<release-highlights>> and <<es-release-notes>>.
+
+As {es} introduces new features and improves existing ones, the changes
+sometimes make older settings, APIs, and parameters obsolete. We typically
+deprecate obsolete functionality as part of a release. If possible, we support
+the deprecated functionality for several subsequent releases before removing it.
+This enables applications to continue working unchanged while you prepare to
+migrate away from the deprecated functionality.
+
+To get the most out of {es} and facilitate future upgrades, we strongly
+encourage migrating away from using deprecated functionality as soon as
+possible.
+
+To give you insight into what deprecated features you're using, {es}:
+
+- Returns a `Warn` HTTP header whenever you
+submit a request that uses deprecated functionality.
+- <<deprecation-logging, Logs deprecation warnings>> when
+deprecated functionality is used.
+- <<migration-api-deprecation, Provides a deprecation info API>>
+that scans a cluster's configuration
+and mappings for deprecated functionality.
+
+For more information about {minor-version},
+see the <<release-highlights>> and <<es-release-notes>>.
+For information about how to upgrade your cluster, see <<setup-upgrade>>.