feat: recon.rb configuration file overrides

[c-dilks]

Briefly, what does this PR introduce?

Change the recon.rb config file options:

    -m, --main-config [FILE]         Main Configuration YAML file
                                     Default: config/irt.yaml

    -c, --configs [FILES]...         Configuration YAML file(s), which override the main configuration file
                                     delimit by commas, no spaces
                                     Default: no overriding files

This allows us to have only one "main" config file, along with any number of overriding files.

What kind of change does this PR introduce?

• Bug fix (issue #__)
• New feature (issue #__)
• Documentation update
• Other: __

Please check if this PR fulfills the following:

• Tests for the changes have been added
• Documentation has been added / updated
• Changes have been communicated to collaborators

Does this PR introduce breaking changes? What changes might users need to make to their code?

no

Does this PR change default behavior?

no