[Feature] - Add order/priority of the Configuration Sources to the configuration

[heiko-holz]

Is your feature request related to a problem? Please describe.
As a user of inspectIT, I'd like to define the order (priority) of the Configuration Sources in the config as well.

Currently, if we use Java agent arguments/Java system properties/environment variables, we need to restart the service before new values apply to the configuration as we cannot overrule the values in the configuration.

Describe the solution you'd like
I'd like to configure the order/priority of the configuration sources directly in the config. The current order can be added to the default config as a fallback

[danipaniii]

In the given graph (SpringBootAppStartUpEvents.pdf) we can observe how the spring boot application starts up and when the different property sources get loaded.
After finding the video: https://www.youtube.com/watch?v=uof5h-j0IeE&t=4700s (starting from 1:18:00) it looks like there is a chance to partially change the property source order, but for it to take effect, the application needs to be restarted, which is the behavior we want to fix. So in my current knowledge I doubt that it will be possible to change the property source order while runtime.