Bug 1551738: [try-staging] Add release-to-esr migration for staging release; r=Callek

Differential Revision: https://phabricator.services.mozilla.com/D31185

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

tools/tryselect/selectors/release.py

@@ -37,7 +37,12 @@ class ReleaseParser(BaseTryParser):
          {'metavar': 'STR',
           'action': 'append',
           'dest': 'migrations',
-          'choices': ['central-to-beta', 'beta-to-release', 'early-to-late-beta'],
+          'choices': [
+              'central-to-beta',
+              'beta-to-release',
+              'early-to-late-beta',
+              'release-to-esr',
+          ],
           'help': "Migration to run for the release (can be specified multiple times).",
           }],
         [['--no-limit-locales'],