Truncate detect strings to 255 characters

An issue raised on GitHub [1] shows that detect strings over 255 characters
cause a non-obvious error to occur during staging of an application. The
commit causes detect strings over 255 characters to be truncated to 252
characters and have an ellipsis appended (...).

[1] https://github.com/cloudfoundry/java-buildpack/issues/58

[#73628824]