Update test to use randomKeyValue for keys & values instead of randomstring

[Uk1288]

Previously the test was using randomstring to generate key & value strings. The api expects keys & values to start with letter or underscore but the randomstringperiodically generates strings starting with numbers. randomstring has been replaced with randomKeyValue which always starts with a letter.

=== FAIL: . TestPolicySetParametersDelete (1.60s)
    helper_test.go:976: invalid attribute
        
        Key must start with a letter or underscore (_). Use only letters, numbers, and underscores.

=== FAIL: . TestPolicySetParametersDelete (re-run 1) (1.57s)
    helper_test.go:976: invalid attribute
        
        Key must start with a letter or underscore (_). Use only letters, numbers, and underscores.

=== FAIL: . TestPolicySetParametersDelete (re-run 2) (1.65s)
    helper_test.go:976: invalid attribute
        
        Key must start with a letter or underscore (_). Use only letters, numbers, and underscores.

=== FAIL: . TestPolicySetParametersDelete (re-run 3) (1.52s)
    helper_test.go:976: invalid attribute
        
        Key must start with a letter or underscore (_). Use only letters, numbers, and underscores.

[Maed223]

Makes sense and looking good!

[github-actions]

Reminder to the contributor that merged this PR: if your changes have added important functionality or fixed a relevant bug, open a follow-up PR to update CHANGELOG.md with a note on your changes.