Add inviting teammates to Create group page

What does this MR do?

• Adds the invite members fields on creating a new group for ee as described in #219241
• Fixes mattermost form alignment
• Tracks the successful invitations that use the GroupInviteMembers concern.

Test Locally

Sign in and visit: http://127.0.0.1:3000/groups/new

Screenshots (strongly suggested)

Inviting members

platform	before	after
desktop
mobile

Fixing mattermost alignment

before	after

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

Related to #219241