Adding docs for preventing invite members to group/project

Smriti Gargrequested to merge
smriti-521362/docs_application_setting_to_disable_invite_users into master

What does this MR do and why?

Deals with documentation for the feature introduced with MR - !189954 (merged)

We introduced a new application setting with name - Disable Group invite members as part of the earlier MR. If this setting is checked, group owner or maintainer will not be able to view buttons Invite members or Invite groups on the pages group>members or project>members.

We need to update docs at right places for user to figure out this new feature

Edited by Smriti Garg

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