Feat/environment variables in workflow (#6515)

Co-authored-by: JzoNg <jzongcode@gmail.com>

api/core/app/segments/parser.py

@@ -0,0 +1,17 @@
+import re
+
+from core.app.segments import SegmentGroup, factory
+from core.workflow.entities.variable_pool import VariablePool
+
+VARIABLE_PATTERN = re.compile(r'\{\{#([a-zA-Z0-9_]{1,50}(?:\.[a-zA-Z_][a-zA-Z0-9_]{0,29}){1,10})#\}\}')
+
+
+def convert_template(*, template: str, variable_pool: VariablePool):
+    parts = re.split(VARIABLE_PATTERN, template)
+    segments = []
+    for part in parts:
+        if '.' in part and (value := variable_pool.get(part.split('.'))):
+            segments.append(value)
+        else:
+            segments.append(factory.build_segment(part))
+    return SegmentGroup(segments=segments)