charts: render multiline strings using block-style

This changed is added because multi-line strings are an issue in
rendered charts since Jinja "commands" are split.

This fix is needed to properly add and render DEX charts as done
in the next commit

charts/render.py

@@ -18,10 +18,13 @@
   `app.kubernetes.io/component` fields
 '''
 
+import re
 import sys
 import subprocess
 
 import yaml
+from yaml.dumper import SafeDumper
+from yaml.representer import SafeRepresenter
 
 
 BOILERPLATE = '''
@@ -65,12 +68,35 @@ def fixup_dict(doc):
 
     return dict((key, fixup_doc(value)) for (key, value) in doc.items())
 
+# Represent multiline strings as literal blocks {{{
+class multiline_str(str): pass
+
+def representer_multiline_str(dumper, data):
+    scalar = SafeRepresenter.represent_str(dumper, data)
+    scalar.style = '|'
+    return scalar
+
+SafeDumper.add_representer(multiline_str, representer_multiline_str)
+
+def fixup_string(value):
+    if '\n' in value:
+        # Remove empty lines
+        value = '\n'.join(
+            line for line in value.splitlines()
+            if not re.match('^\s*$', line)
+        )
+        return multiline_str(value)
+    return value
+# }}}
+
 
 def fixup_doc(doc):
     if isinstance(doc, dict):
         return fixup_dict(doc)
     elif isinstance(doc, list):
         return [fixup_doc(d) for d in doc]
+    elif isinstance(doc, str):
+        return fixup_string(doc)
     else:
         return doc