Bug 1529848 - increase maximum length for task identifiers to 38 r=tomprince

Changes:

- increase maximum length for task identifiers to 38 from 22
- update documentation to state the same

Differential Revision: https://phabricator.services.mozilla.com/D20785

--HG--
extra : moz-landing-system : lando

taskcluster/taskgraph/transforms/task.py

@@ -1793,9 +1793,9 @@ def chain_of_trust(config, tasks):
 @transforms.add
 def check_task_identifiers(config, tasks):
     """Ensures that all tasks have well defined identifiers:
-       ^[a-zA-Z0-9_-]{1,22}$
+       ^[a-zA-Z0-9_-]{1,38}$
     """
-    e = re.compile("^[a-zA-Z0-9_-]{1,22}$")
+    e = re.compile("^[a-zA-Z0-9_-]{1,38}$")
     for task in tasks:
         for attr in ('workerType', 'provisionerId'):
             if not e.match(task['task'][attr]):