Upgrade to symfony 7 for CMS 6

[GuySartorelli]

As per our major support policy

At launch, Silverstripe CMS major releases track the latest stable major version of Symfony dependencies.

For CMS 6, this means upgrading from symfony 6 to symfony 7.

kitchen-sink ci

• https://github.com/creative-commoners/recipe-kitchen-sink/actions/runs/10660288256

PRs

• DEP Upgrade to symfony 7 silverstripe-assets#636
• DEP Upgrade to symfony 7 silverstripe-behat-extension#283
• DEP Upgrade to symfony 7 silverstripe-config#122
• DEP Upgrade to symfony 7 silverstripe-event-dispatcher#28
• DEP Upgrade to symfony 7 silverstripe-framework#11356
• DEP Upgrade to symfony 7 silverstripe-graphql-devtools#57
• DEP Remove old symfony conflicts recipe-testing#26
• DEP Upgrade to symfony 7 silverstripe-session-manager#218
• DEP Upgrade to symfony 7 silverstripe-versioned#470
• DEP Upgrade to symfony 7 symbiote/silverstripe-advancedworkflow#551
• DOC Updated symfony dependencies developer-docs#574

[GuySartorelli]

@emteknetnz Please add an entry to the changelog about this, and double check if any other docs need to be updated.

[emteknetnz]

Done silverstripe/developer-docs#574

[GuySartorelli]

Changes required in silverstripe/silverstripe-framework#11356

[GuySartorelli]

PRs merged