Rate limits, Flow control - no validation if "count by" field key is empty

[olgasobolevsky]

Describe the bug Can create and save without warning rate limit rule with "Count by: Header/Argument/Cookie" name - empty.

To Reproduce Steps to reproduce the behavior:

1. Go to Rate limits -> create rate limit.
2. Fill all the fields, "Count by" - choose "Header", header name leave empty (delete the default value). Save.
3. New rule created with "Count by: Header" with empty name.

Expected behavior Warning/ error message (for example: "Can't create rule with empty key name")

Desktop (please complete the following information):

• OS: Mac Os
• Browser chrome

• Same bug for Flow Control