feat: add capitalization rule for colons in headings

.vale/styles/Google/Colons.yml

@@ -3,5 +3,6 @@ message: "'%s' should be in lowercase."
 link: 'https://developers.google.com/style/colons'
 nonword: true
 level: warning
+scope: sentence
 tokens:
   - ':\s[A-Z]'

.vale/styles/Google/HeadingColons.yml

@@ -0,0 +1,8 @@
+extends: existence
+message: "'%s' should be in uppercase."
+link: 'https://developers.google.com/style/capitalization#capitalization-in-titles-and-headings'
+nonword: true
+level: warning
+scope: heading
+tokens:
+  - ':\s[a-z]'

.vale/styles/Google/Headings.yml

@@ -4,6 +4,8 @@ link: 'https://developers.google.com/style/capitalization#capitalization-in-titl
 level: warning
 scope: heading
 match: $sentence
+indicators:
+  - ':'
 exceptions:
   - Azure
   - CLI