fix(logwriter): tighten up parameter patterns (#320)

`LogGroupNamePatterns` and `LogGroupNamePrefixes` do not support regular
expressions. Constraining the allowed pattern for either parameter
ensures we error out early if a user attempts to pass in a regular
expression.

apps/logwriter/template.yaml

@@ -64,13 +64,15 @@ Parameters:
       `DescribeLogGroups` action for more information.
       To subscribe to all log groups, use the wildcard operator *.
     Default: ''
+    AllowedPattern: '^(\*|[a-zA-Z0-9-_\/]*)$'
   LogGroupNamePrefixes:
     Type: CommaDelimitedList
     Description: >-
       Comma separated list of prefixes. The lambda function will only apply to
       log groups that start with a provided string. To subscribe to all log
       groups, use the wildcard operator *.
     Default: ''
+    AllowedPattern: '^(\*|[a-zA-Z0-9-_\/]*)$'
   ExcludeLogGroupNamePatterns:
     Type: CommaDelimitedList
     Description: >-

apps/stack/template.yaml

@@ -89,12 +89,14 @@ Parameters:
       only apply to log groups that have names that match one of the provided
       strings based on a case-sensitive substring search.
     Default: ''
+    AllowedPattern: '^(\*|[a-zA-Z0-9-_\/]*)$'
   LogGroupNamePrefixes:
     Type: CommaDelimitedList
     Description: >-
       Comma separated list of prefixes. If not empty, the lambda function will
       only apply to log groups that start with a provided string.
     Default: ''
+    AllowedPattern: '^(\*|[a-zA-Z0-9-_\/]*)$'
   ExcludeLogGroupNamePatterns:
     Type: CommaDelimitedList
     Description: >-