PS-10482 [DOCS] - Create a What's Changed in the MySQL 9.x series document 8.4

	new file:   docs/9x-breaking-changes.md
	new file:   docs/9x-compatibility-and-removed-items.md
	new file:   docs/9x-defaults-and-tuning.md
	modified:   docs/index.md
	modified:   docs/installation.md
	modified:   docs/upgrade.md
	new file:   docs/whats-new-mysql-9x-apt-dnf-yum.md
	new file:   docs/whats-changed-mysql-9x.md
	modified:   mkdocs-base.yml

Author: patrickbirch

docs/index.md

@@ -62,6 +62,12 @@ Upgrade your Percona Server for MySQL installation with our comprehensive upgrad
 
 </div><div data-banner markdown>
 
+### :material-information-outline: Planning for the MySQL 9.x series? { .title }
+
+If you are evaluating or planning a move to the MySQL 9.x series (for example, Percona Server for MySQL 9.7 LTS), see [What's New in MySQL 9.x: Technical Migration Overview](whats-new-mysql-9.md) for breaking changes, compatibility, removed items, and defaults and tuning.
+
+</div><div data-banner markdown>
+
 ## :fontawesome-solid-gears: Audit Log Filter plugin { .title }
 
 Learn about the Audit Log Filter plugin that allows you to monitor, log, and block a connection or query actively executed on the selected server.

docs/installation.md

@@ -12,6 +12,8 @@ The following guides describe the installation process for using the official Pe
 
 [Install Percona Server for MySQL on Debian and Ubuntu](apt-repo.md){.md-button}        [Install Percona Server for MySQL on Red Hat Enterprise Linux](yum-repo.md){.md-button}
 
+If you are considering the MySQL 9.x series (for example, Percona Server for MySQL 9.7 LTS via APT, DNF, or YUM), see [What's New in MySQL 9.x: Technical Migration Overview](whats-new-mysql-9.md) for breaking changes, compatibility, removed items, and defaults and tuning.
+
 ## Other installation methods
 
 [Install Percona Server for MySQL from Binaries](binary-tarball-install.md){.md-button} <br>       [Compile Percona Server for MySQL from Source](source-tarball.md){.md-button} <br>       [Run Percona Server for MySQL in a Docker container](docker.md){.md-button} 

docs/upgrade.md

@@ -49,6 +49,8 @@ Review these documents to understand breaking changes, removed features, and com
 
 * [Percona Toolkit updates for {{vers}}](./percona-toolkit-8.4-updates.md) - Review toolkit changes if you use Percona Toolkit
 
+If you are planning an upgrade to the MySQL 9.x series (for example, to Percona Server for MySQL 9.7 LTS), see [What's New in MySQL 9.x: Technical Migration Overview](./whats-new-mysql-9.md) for breaking changes, compatibility, removed items, and defaults and tuning.
+
 ### Step 2: Complete pre-upgrade preparation
 
 Work through the pre-upgrade checks in the [upgrade checklist](./upgrade-checklist-8.4.md). This includes:
@@ -137,12 +139,10 @@ Review these upgrade-related documents:
 * [Downgrade options](./downgrade.md)
 
 * [Breaking and incompatible changes in {{vers}}](./8.4-breaking-changes.md)
-
 * [Compatibility and removed items in {{vers}}](./8.4-compatibility-and-removed-items.md)
-
 * [Defaults and tuning guidance for {{vers}}](./8.4-defaults-and-tuning.md)
-
 * [Percona Toolkit updates for {{vers}}](./percona-toolkit-8.4-updates.md)
+* [What's New in MySQL 9.x: Technical Migration Overview](./whats-new-mysql-9.md) (for migration to 9.x / 9.7 LTS)
 
 ### Additional MySQL documentation