Bug 1816445: improve defaults to release promotion action task r=jcristau

Two main issues I've found:
1) release_promotion_flavor is required, but has no default, so it doesn't show up in the default list of fields
2) The decision task ended up failing because partner repacks were enabled, but I didn't provide partner repack config. We should default these to disabled (any production use case explicitly sets them, so this should be harmless and no-opt to those).

Differential Revision: https://phabricator.services.mozilla.com/D169639

taskcluster/gecko_taskgraph/actions/release_promotion.py

@@ -119,6 +119,7 @@ def get_flavors(graph_config, param):
             "release_promotion_flavor": {
                 "type": "string",
                 "description": "The flavor of release promotion to perform.",
+                "default": "FILL ME OUT",
                 "enum": sorted(graph_config["release-promotion"]["flavors"].keys()),
             },
             "rebuild_kinds": {
@@ -205,10 +206,12 @@ def get_flavors(graph_config, param):
             },
             "release_enable_partner_repack": {
                 "type": "boolean",
+                "default": False,
                 "description": "Toggle for creating partner repacks",
             },
             "release_enable_partner_attribution": {
                 "type": "boolean",
+                "default": False,
                 "description": "Toggle for creating partner attribution",
             },
             "release_partner_build_number": {
@@ -239,6 +242,7 @@ def get_flavors(graph_config, param):
             },
             "release_enable_emefree": {
                 "type": "boolean",
+                "default": False,
                 "description": "Toggle for creating EME-free repacks",
             },
             "required_signoffs": {
@@ -369,11 +373,9 @@ def release_promotion_action(parameters, graph_config, input, task_group_id, tas
         release_enable_emefree = False
     else:
         # for promotion or ship phases, we use the action input to turn the repacks/attribution off
-        release_enable_partner_repack = input.get("release_enable_partner_repack", True)
-        release_enable_partner_attribution = input.get(
-            "release_enable_partner_attribution", True
-        )
-        release_enable_emefree = input.get("release_enable_emefree", True)
+        release_enable_partner_repack = input["release_enable_partner_repack"]
+        release_enable_partner_attribution = input["release_enable_partner_attribution"]
+        release_enable_emefree = input["release_enable_emefree"]
 
     partner_url_config = get_partner_url_config(parameters, graph_config)
     if (