Update Drupal Symfony Mailer from ~2.0 to ~2.3.0 and remove enabling Symfony Mailer Override Backward Compatibility sub module

Problem/Motivation

Drupal Symfony Mailer 1.3.0-beta1 was released on 7 May 2023 by: AdamPS
https://www.drupal.org/project/symfony_mailer/releases/1.3.0-beta1

#3355626: Obsolete the symfony_mailer_bc module

Previously, the purpose of enabling the symfony_mailer_bc module was to enable all override. Since #3315358: Allow full management of override plugins we can enable overrides one by one, so we no longer need the sub-module.

• #3315358: Allow full management of override plugins
• #3359917: Drupal 10 deprecations
• #3355846: Circular reference on multi-language sites

Proposed resolution

• Change drupal/symfony_mailer to ~1.3.0 in the composer.json file.
• Remove symfony_mailer_bc from the varbase_email.info.yml
• Add default mailer policy configs and mailer transport config for Varbase
• Add a hook update to uninstall symfony_mailer_bc Only if it was enabled
  

  Only to make sure when upgrading from 9.0.x to 10.0.x for sites which did not switch from Swiftmailer to Symfony Mailer or switched to an older branch.

Remaining tasks

• ✅ File an issue about this project
• ✅ Addition/Change/Update/Fix to this project
• ✅ Testing to ensure no regression
• ➖ Automated unit/functional testing coverage
• ✅ Developer Documentation support on feature change/addition
  
  Changed
  Configure Symfony Mailer
• ➖ User Guide Documentation support on feature change/addition
• ➖ Accessibility and Readability
• ✅ Code review from 1 Varbase core team member
• ✅ Full testing and approval
• ✅ Credit contributors
• ✅ Review with the product owner
• ✅ Update Release Notes and Update Helper on new feature change/addition
• ✅ Release Varbase 10.0.0-alpha2, varbase_email-10.0.0-alpha2

Varbase update type

• ✅ No Update
• ➖ Optional Update
• ➖ Forced Update
• ➖ Forced Update if Unchanged

User interface changes

• N/A

API changes

• N/A

Data model changes

• N/A

Release notes snippet

• Issue #3364734: Updated Drupal Symfony Mailer from ~2.0 to ~2.3.0 and removed enabling Symfony Mailer Override Backward Compatibility sub module
  
  Changed
  Configure Symfony Mailer