Add ability to fail fast by throwing an exception if a property is absent

[ashtttt]

I am trying to use @EnvironmentVariable annotation, currently if annotated environment variable is not set in the deployed environment the fields are left with "null" value.
I can see we have option to set a default value, can we also have an option to throw an exception if a given environment variable is not set. This allows us to fail the applications during configuration initialization.

[fmbenhassine]

Makes sense, as there is no way to fail fast currently. This can actually be added to all annotations. Let me plan this for next release. Thank you for raising this issue!

[fmbenhassine]

@ashtttt I added the ability to fail fast by throwing an exception if an environment variable is not set:

class Bean {
     @EnvironmentVariable(value = "absent", failFast = true)
     private String absentValue;
}

You can try it already with v3.1.0-SNAPSHOT.

Thank you for raising this issue!