Add /logfile MVC actuator endpoint

Add a `/logfile` endpoint which can be used to fetch the contents of
the log file (if one is being used).

Fixes gh-2137
Closes gh-2294

spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc

@@ -643,6 +643,9 @@ content into your application; rather pick only the properties that you need.
 	endpoints.info.id=info
 	endpoints.info.sensitive=false
 	endpoints.info.enabled=true
+	endpoints.logfile.path=/logfile
+	endpoints.logfile.sensitive=true
+	endpoints.logfile.enabled=true
 	endpoints.mappings.enabled=true
 	endpoints.mappings.id=mappings
 	endpoints.mappings.sensitive=true

spring-boot-docs/src/main/asciidoc/production-ready-features.adoc

@@ -94,6 +94,11 @@ unauthenticated connection or full message details when authenticated).
 |Displays arbitrary application info.
 |false
 
+|`logfile`
+|Returns the contents of the logfile (if `logging.file` or `logging.path` properties have
+been set). Only available via MVC.
+|true
+
 |`metrics`
 |Shows '`metrics`' information for the current application.
 |true