Adding indicator_prefix to CAN

Required, currently manually provided in https://github.com/cmu-delphi/covidcast-indicators/blob/0943e38f4a7e5a33d521f0f807313059f4c8e300/covid_act_now/delphi_covid_act_now/run.py#L53. needed to be provided to avoid https://github.com/cmu-delphi/covidcast-indicators/blob/f83033786a912c475e53654a2bc58c2d067e2727/_delphi_utils_python/delphi_utils/archive.py#L143

Author: qx-teo

ansible/templates/covid_act_now-params-prod.json.j2

@@ -9,6 +9,7 @@
   "archive": {
     "cache_dir": "./cache",
     "bucket_name": "delphi-covidcast-indicator-output",
+    "indicator_prefix": "CAN",
     "aws_credentials": {
       "aws_access_key_id": "{{ delphi_aws_access_key_id }}",
       "aws_secret_access_key": "{{ delphi_aws_secret_access_key }}"

covid_act_now/params.json.template

@@ -9,6 +9,7 @@
   "archive": {
     "cache_dir": "./cache",
     "bucket_name": "",
+    "indicator_prefix": "CAN",
     "aws_credentials": {
       "aws_access_key_id": "",
       "aws_secret_access_key": ""