chore(web-analytics): Simplify channel type and reference docs (#21196)

* Simply channel type and reference docs

* Fix quotes type

posthog/hogql/database/schema/channel_type.py

@@ -68,14 +68,17 @@ def wrap_with_null_if_empty(expr: ast.Expr) -> ast.Expr:
             args=[ast.Call(name="nullIf", args=[expr, ast.Constant(value="")]), ast.Constant(value="null")],
         )
 
+    # This logic is referenced in our docs https://posthog.com/docs/data/channel-type, be sure to update both if you
+    # update either.
     return parse_expr(
         """
 multiIf(
     match({campaign}, 'cross-network'),
     'Cross Network',
 
     (
-        match({medium}, '^(.*cp.*|ppc|retargeting|paid.*)$') OR
+        {medium} IN ('cpc', 'cpm', 'cpv', 'cpa', 'ppc', 'retargeting') OR
+        startsWith({medium}, 'paid') OR
         {gclid} IS NOT NULL OR
         {gad_source} IS NOT NULL
     ),