Make Flag text sentence case by default (#33)

* Per design, flag text should be sentence case

* Add support to customize the case style.

amundsen_application/static/js/components/common/Flag/index.tsx

@@ -3,20 +3,41 @@ import * as React from 'react';
 // TODO: Use css-modules instead of 'import'
 import './styles.scss';
 
+enum CaseType {
+  LOWER_CASE = 'lowerCase',
+  SENTENCE_CASE = 'sentenceCase',
+  UPPER_CASE = 'upperCase',
+}
+
 interface FlagProps {
+  caseType?: string | null;
   text: string;
   labelStyle?: string;
 }
 
-const Flag: React.SFC<FlagProps> = ({ text, labelStyle }) => {
+function convertText(str: string, caseType: string): string {
+  switch (caseType) {
+    case CaseType.LOWER_CASE:
+      return str.toLowerCase();
+    case CaseType.SENTENCE_CASE:
+      return `${str.charAt(0).toUpperCase()}${str.slice(1).toLowerCase()}`;
+    case CaseType.UPPER_CASE:
+      return str.toUpperCase();
+    default:
+      return str;
+  }
+}
+
+const Flag: React.SFC<FlagProps> = ({ caseType, text, labelStyle }) => {
   // TODO: After upgrading to Bootstrap 4, this component should leverage badges
   // https://getbootstrap.com/docs/4.1/components/badge/
   return (
-    <span className={`flag label ${labelStyle}`}>{text.toUpperCase()}</span>
+    <span className={`flag label ${labelStyle}`}>{convertText(text, caseType)}</span>
   );
 };
 
 Flag.defaultProps = {
+  caseType: null,
   text: '',
   labelStyle: 'label-default',
 };