Populate tag list in contact webhooks (#6861)

[Clement134]

Please be sure you are submitting this against the staging branch.

Q	A
Bug fix?	Yes
New feature?	No
Automated tests included?	No
Related user documentation PR URL	No
Related developer documentation PR URL	No
Issues addressed (#s or URLs)	#6861
BC breaks?	No
Deprecations?	No

Description:

At the moment, tag list in the contact webhooks contains only empty objects. This PR, populate tag list with tag's data.

Steps to reproduce the bug:

1. Create webhook for "Contact Updated Event", "Contact subscription change" and "Contact point change"
2. Trigger each webhooks for a tagged contact
3. Check webhook's payload (with empty tag array)

Steps to test this PR:

1. Create webhook for "Contact Updated Event", "Contact subscription change" and "Contact point change"
2. Trigger each webhooks for a tagged contact
3. Check webhook's payload, tags array should be populated with tag's data

List deprecations along with the new alternative:

No deprecations

List backwards compatibility breaks:

No backwards compatibility breaks

[kuzmany]

Can you fix the travis check? Looks like error with unit test (Mautic\LeadBundle\Tests\EventListener\WebhookSubscriberTest::testChannelChangeIsPickedUpByWebhook)
https://travis-ci.org/mautic/mautic/jobs/456576272#L671