Add java sample to CD/Secret Management

[scgbear]

Is your feature request related to a problem? Please describe.
Would be more comprehensive to include a java example along with the Python C# and Node example on this page: https://github.com/microsoft/code-with-engineering-playbook/tree/main/docs/continuous-delivery/secrets-management

Describe the solution you'd like
Following the same convention defined by the other language examples it shouldn't be much more than a .env with a reference to a library to load the .env file such as https://github.com/cdimascio/dotenv-java

Describe alternatives you've considered
NA

Additional context
NA