feat: updated build to jdk 11

[akafredperry]

- What I did
Updated so that SDK (and other modules) are now compiled with JDK 11.
close #322

- How I did it

• Adjusted parent pom properties
• Updated jackson and slf4j versions
• Updated all READMEs to reflect these changes and other recent changes. Instructions for running CLI utilities now uses maven exec java plugin (which simplifies the classpath setup)
• Fixed at_shell shaded / fatjar for JDK 11
• Cleaned up CLI utilities, less code and demonstrates how AtClients are Closeable and should be used within a try catch
• Adjusted ConfigReader so that it works with exec:java plugin
• Adjusted github wofklows

- How to verify it
Run all the tests

mvn clean verify

I have run the various CLI and checked that the codeblocks in the README actually work.
pymarkdown has been run against all README markdown

- Description for the changelog
update to jdk 11