Update monolog configuration to use dynamic log prefix and add error log handler

Revised `monolog.yaml` to replace static `log_prefix` with `chill_environment` variable and added a new `errors_log` handler. Expanded exclusion channels in default handler to include `deprecation`.

templates/config/prod/monolog.yaml

@@ -6,7 +6,7 @@
 #
 
 parameters:
-  log_prefix: 'test'
+  log_prefix: '{{ chill.chill_environment }}'
 monolog:
   # make a "notifier" channel available
   channels: ['notifier']
@@ -16,6 +16,10 @@ monolog:
       path: "%kernel.logs_dir%/notifier-%log_prefix%.log"
       level: info
       channels: [ 'notifier' ]
+    errors_log:
+      type: stream
+      path: "%kernel.logs_dir%/error-%log_prefix%.log"
+      level: error
     privacy_log:
       type: stream
       path: "%kernel.logs_dir%/privacy-%log_prefix%.log"
@@ -25,7 +29,7 @@ monolog:
       type: stream
       path: "%kernel.logs_dir%/default-%log_prefix%.log"
       level: info
-      channels: [ '!event', '!doctrine', '!console', '!chill',]
+      channels: [ '!event', '!doctrine', '!console', '!chill', '!deprecation']
     console:
       type: console
       process_psr_3_messages: false