In a properties file, a backslash is used as an escape character for
the line terminator sequence to allow values to be split across
multiple lines. When a backslash is used elsewhere they're stripped
out of the property's value.

This commit updates .properties-based examples for configuring
server.tomcat.internal-proxies to escape the backslahes so that they
are retained in the property's value at runtime.

See gh-1989