Enable collection user management tab in CCSM UI with new UIConfiguration flag

Context:
Once the BE has implemented user search with identity for CCSM, we can enable the collection user management in the UI for CCSM in the FE in environments where the identity user search is available. Note that identity is currently implementing a feature that, if used, disables user search.
BE is adding a new flag in the UIConfiguration to use for the FE to determine whether or not user search functionality is to be hidden in the UI. Suggested name of flag: userSearchAvailable. If true, user search UI it to be displayed. If false, user search UI is to be hidden.

Because identity doesn't yet implement group retrieval, the modal heading also needs adjusted in CCSM because users can only search for users, not user groups. 

AT:

• display of collections user tab is made dependent on UIConfiguration  userSearchAvailable flag:
  • If true, users tab is shown and users can be managed as is already implemented for C7/SaaS
  • if false, users tab is hidden 
• When users tab is displayed in CCSM, it is adjusted to groups not being available:
  • header of tab, table and "add" modal only says "users"/"search users" etc
  • users table hides the "members" column

Testing Notes:

Collection user management exists in CCSM and works the same as in SaaS and C7 if identity is run with keycloak.

How to set up additional users when testing locally:

1. Start zeebe, keycloak, identity (working docker-compose attached. If it doesnt work try restarting identity after keycloak is already running)
2. Add new user in keycloak:
   1. access keycloak
   2. select "camunda-platform realm" from realm dropdown
   3. select "users" from menu
   4. Add new user
3. Configure missing role permission in identity (coming automatically with https://github.com/camunda-cloud/identity/issues/2278)
   1. access identity
   2. go to "Roles" tab
   3. click on  "Optimize" role
   4. go to "permissions" tab
   5. Click "assign permission" and add "[read:users]" permission
4. Configure new user in identity:
   1. access identity
   2. go to "users" tab
   3. click on new user
   4. go to "assigned roles" and add Optimize
5. Start Optimize and confirm FE behaviour:

1. 1. Adding new user to collection works as expected with user add modal
   2. displaying users in collection user tab table works as expected
   3. If new user is removed from keycloak is removed from the user in identity after having been added to collection, user is only shown with userID (not fullname) in collection users tab and no longer appears in searches