minor #29077 Add framework asset changes to upgrade 3.0 guide (KatharinaSt)

This PR was squashed before being merged into the 2.8 branch (closes #29077).

Discussion
----------

Add framework asset changes to upgrade 3.0 guide

| Q             | A
| ------------- | ---
| Branch?       | 2.8 up to 4.1 <!-- see below -->
| Bug fix?      | no (upgrade guide improvement)
| New feature?  | no <!-- don't forget to update src/**/CHANGELOG.md files -->
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no <!-- don't forget to update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets | #29050   <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        | - <!-- required for new features -->

further reading:
https://symfony.com/blog/new-in-symfony-2-7-the-new-asset-component
<!--
Write a short README entry for your feature/bugfix here (replace this comment block.)
This will help people understand your PR and can be used as a start of the Doc PR.
Additionally:
 - Bug fixes must be submitted against the lowest branch where they apply
   (lowest branches are regularly merged to upper ones so they get the fixes too).
 - Features and deprecations must be submitted against the master branch.
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Commits
-------

7de10880a4 Add framework asset changes to upgrade 3.0 guide

UPGRADE-2.7.md

@@ -646,6 +646,34 @@ FrameworkBundle
    }
    ```
 
+ * The assets settings under `framework.templating` were deprecated and will be removed in Symfony 3.0. Use `framework.assets` instead.
+
+   Before:
+
+   ```yml
+   framework:
+       templating:
+           assets_version: 'v123'
+           assets_version_format: '%%s?version=%%s'
+           assets_base_urls:
+               http: ['http://cdn.example.com']
+               ssl:  ['https://secure.example.com']
+           packages:
+               # ...
+   ```
+
+   After:
+
+   ```yml
+   framework:
+       assets:
+           version: 'v123'
+           version_format: '%%s?version=%%s'
+           base_urls: ['http://cdn.example.com', 'https://secure.example.com']
+           packages:
+               # ...
+   ```
+
 Security
 ---------------
 

UPGRADE-3.0.md

@@ -883,6 +883,34 @@ UPGRADE FROM 2.x to 3.0
            engines: ['php']
    ```
 
+ * The assets settings under `framework.templating` were moved to `framework.assets`.
+
+   Before:
+
+   ```yml
+   framework:
+       templating:
+           assets_version: 'v123'
+           assets_version_format: '%%s?version=%%s'
+           assets_base_urls:
+               http: ['http://cdn.example.com']
+               ssl:  ['https://secure.example.com']
+           packages:
+               # ...
+   ```
+
+   After:
+
+   ```yml
+   framework:
+       assets:
+           version: 'v123'
+           version_format: '%%s?version=%%s'
+           base_urls: ['http://cdn.example.com', 'https://secure.example.com']
+           packages:
+               # ...
+   ```
+
  * The `form.csrf_provider` service is removed as it implements an adapter for
    the new token manager to the deprecated
    `Symfony\Component\Form\Extension\Csrf\CsrfProvider\CsrfProviderInterface`