[SwiftMailer] send error log mails from CLI

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT

Given I have symfony2 application with Monolog configured to send mail on error logs.
When I have exception thrown from CLI task
Then I should receive error mail

However this is not true because `Monolog/SwiftMailerHandler` is doing force flush only on `kernel.terminate`, but not on `console.terminate`

This PR fixes issue together with https://github.com/symfony/symfony/pull/10534