MP-JWT configuration property name with dot (.)

[chunlongliang-ibm]

MP-JWT configuration property name contains dot (.), like mp.jwt.verify.publickey.location. However, you can not define mp.jwt.verify.publickey.location as environment variable in some OS, for example Ubuntu. See https://unix.stackexchange.com/questions/93532/exporting-a-variable-with-dot-in-it

We should consider to change the naming convention in the future, and/or update spec to exclude the use of environment variables.

MP-Config 1.3 realize the existence of disallowed environment variable, and it will search a variable by replacing dot (.) with under score (_). see https://github.com/eclipse/microprofile-config/blob/master/spec/src/main/asciidoc/configsources.asciidoc.

[starksm64]

I have added a "Mapping Properties to Environment Variables" section to the spec that provides the rules MP config uses when searching for a property with a '.' in its name among environment variables, and provide a table of the valid mappings.