Auto detect log format

.changesets/auto-detect-log-format.md

@@ -0,0 +1,11 @@
+---
+bump: patch
+type: change
+---
+
+Detect the log format automatically. We now detect if a log line is in the JSON, Logfmt or plaintext formats. No further config needed when calling our logger, like so:
+
+```ruby
+logger = Appsignal::Logger.new("gruop")
+logger.info("message")
+```

lib/appsignal/logger.rb

@@ -53,6 +53,8 @@ def to_proc
     # @!visibility private
     JSON = 2
     # @!visibility private
+    AUTODETECT = 3
+    # @!visibility private
     SEVERITY_MAP = {
       DEBUG => 2,
       INFO => 3,
@@ -73,7 +75,7 @@ def to_proc
     # @param format [Integer] Format to use to parse log line attributes.
     # @param attributes [Hash<String, String>] Default attributes for all log lines.
     # @return [void]
-    def initialize(group, level: INFO, format: PLAINTEXT, attributes: {})
+    def initialize(group, level: INFO, format: AUTODETECT, attributes: {})
       raise TypeError, "group must be a string" unless group.is_a? String
 
       @group = group

sig/appsignal.rbi

@@ -1318,7 +1318,7 @@ module Appsignal
         attributes: T::Hash[String, String]
       ).void
     end
-    def initialize(group, level: INFO, format: PLAINTEXT, attributes: {}); end
+    def initialize(group, level: INFO, format: AUTODETECT, attributes: {}); end
 
     # Sets the formatter for this logger and all broadcasted loggers.
     #