Enable integration_form_refactor by default

What does this MR do?

The feature flag integration_form_refactor can now be enabled by default now that all work around the refactor has been done. This has been enabled on GitLab.com production since 2020-06-15 (link, internal) without any issues reported.

This will allow self-hosted users to to use the new form and report issues (if any). At the next milestone if there are not issues reported, we will proceed to remove the feature flag completely.

Previous MRs related to the feature flag (in chronological order):

Title	Link
Update Active checkbox component to use toggle	!27778 (merged)
Update Jira comment to include more information	!30258 (merged)
Extract integration trigger fields to Vue	!31074 (merged)
Extract integration custom fields to Vue	!31430 (merged)
Update ActiveToggle and JiraTriggerFields with new form layout	!32677 (merged)
Refine UI of integration form	!34707 (merged)

Screenshots

Integration	Before	After
Slack
Jira

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team