fix: same values but different casing creates conflicting enums

[vinayak-kukreja]

Enums in schema which has same value but different casing creates same enum values which conflicts with each other. For instance, observed while importing a custom resource definition in cdk8s.

\| 1086   REPLACE = 'replace',
--
\|        ~~~~~~~
\| com.coreos.monitoring.ts:1088:3 - error TS2300: Duplicate identifier 'REPLACE'.
\| 1088   REPLACE = 'Replace',
\|        ~~~~~~~
\| com.coreos.monitoring.ts:1090:3 - error TS2300: Duplicate identifier 'KEEP'.
\| 1090   KEEP = 'keep',
\|        ~~~~
\| com.coreos.monitoring.ts:1092:3 - error TS2300: Duplicate identifier 'KEEP'.
\| 1092   KEEP = 'Keep',
\|        ~~~~
\| com.coreos.monitoring.ts:1094:3 - error TS2300: Duplicate identifier 'DROP'.
\| 1094   DROP = 'drop',
\|        ~~~~
\| com.coreos.monitoring.ts:1096:3 - error TS2300: Duplicate identifier 'DROP'.
\| 1096   DROP = 'Drop',

Fixes cdk8s-team/cdk8s-cli#578