Group names are returned in lowercase in the response of REST API

Issue Summary

Though uppercase group name is not allowed to create from Confluence, it can be synced from external directories(LDAP/Jira).

When running below REST APIs, only lowercase group names can be returned, which is not same to original ones in external directories.

GET /rest/api/group
or
GET /rest/api/group/{groupName} 

This is reproducible on Data Center: (yes) 

Note: it is similar one to this cloud ticket 

Steps to Reproduce

1. Create a group with name of "TEST" (uppercase) in external directories(LDAP/Jira).
2. Sync the directory and make above group shown in Confluence.
3. Make a GET REST request to this endpoint `/rest/api/group/TEST`

Expected Results

Original uppercase group name (TEST) should be returned in response.

{"type":"group","name":"TEST","_links":{"base":"http://confluence.abctest.test","context":"","self":"http://confluence.abctest.test/rest/api/group/test"}}%

Actual Results

The group name is converted to lowercase(test).

{"type":"group","name":"test","_links":{"base":"http://confluence.abctest.test","context":"","self":"http://confluence.abctest.test/rest/api/group/test"}}%

Workaround

Currently there is no known workaround for this behavior.