merge custom config with prowler's default config

[kagahd]

New feature motivation

When using prowler with the option --config-file, the given config file replaces prowler's own default config file. Therefore, users have to merge their config with prowler's config on every new release of prowler which is not only quite tedious but can also be forgotten.
Usually, users put in their custom config only those values that they want to match their specific requirements. These values should just overwrite prowlers default config values.
It is counterintuitive to require the user to provide a complete configuration that is already provided by prowler when they only want to specify a few custom configuration values.

Solution Proposed

I suggest that prowler merges both configs by giving precedence the values of the custom config file passed by --config-file. This behaviour must be documented.

Describe alternatives you've considered

I don't see any alternative. At the very least, the behavior of how a user-defined configuration file is used by prowler, i.e. overwriting or replacing, and also the consequences when upgrading prowler should be clearly documented.

Additional context

No response