…abpot)

This PR was merged into the 4.3-dev branch.

Discussion
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[Messenger] Add missing information in messenger logs

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | yes-ish
| New feature?  | yes-ish
| BC breaks?    | no
| 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 | n/a
| License       | MIT
| Doc PR        | n/a

When using `messenger:consume`, I get the following logs:

```
2019-03-25T11:39:05+01:00 [info] Received message "Symfony\Component\Mailer\EnvelopedMessage"
2019-03-25T11:39:05+01:00 [warning] An exception occurred while handling message "Symfony\Component\Mailer\EnvelopedMessage"
2019-03-25T11:39:05+01:00 [info] Retrying Symfony\Component\Mailer\EnvelopedMessage - retry #1.
2019-03-25T11:39:05+01:00 [info] Sending message "Symfony\Component\Mailer\EnvelopedMessage" with "Symfony\Component\Messenger\Transport\AmqpExt\AmqpTransport"
2019-03-25T11:39:06+01:00 [info] Received message "Symfony\Component\Mailer\EnvelopedMessage"
2019-03-25T11:39:06+01:00 [warning] An exception occurred while handling message "Symfony\Component\Mailer\EnvelopedMessage"
2019-03-25T11:39:06+01:00 [info] Retrying Symfony\Component\Mailer\EnvelopedMessage - retry #2.
2019-03-25T11:39:06+01:00 [info] Sending message "Symfony\Component\Mailer\EnvelopedMessage" with "Symfony\Component\Messenger\Transport\AmqpExt\AmqpTransport"
2019-03-25T11:39:09+01:00 [info] Received message "Symfony\Component\Mailer\EnvelopedMessage"
2019-03-25T11:39:09+01:00 [warning] An exception occurred while handling message "Symfony\Component\Mailer\EnvelopedMessage"
2019-03-25T11:39:09+01:00 [info] Retrying Symfony\Component\Mailer\EnvelopedMessage - retry #3.
2019-03-25T11:39:09+01:00 [info] Sending message "Symfony\Component\Mailer\EnvelopedMessage" with "Symfony\Component\Messenger\Transport\AmqpExt\AmqpTransport"
```

So, an. error occurred, but I have no idea what's going on. The exception is in the context, but the context is not displayed by default. So, this PR fixes it.

Commits
-------

20664ca [Messenger] added missing information in messenger logs