configuration file

benefit: have the config in a file, so no CLI parameters are needed

parameter defaults are read from the config-file, and may override system defaults.
parameters can still be overridden via CLI parameters

implementation details: use `extra` section of the composer file.
see https://getcomposer.org/doc/04-schema.md#extra

----

## acc / crit
- [ ] config overrides system defaults (therefore config file settings = presets)
- [ ] CLI params override any defaults/presets
- [ ] parameter type checks are (still) in place
- [ ] parameter plausibility checks are still in place
- [ ] config possibility is documented
(+ docs have hint, that this config can be used with the [gh-action] -- see https://github.com/CycloneDX/gh-php-composer-generate-sbom/issues/1)

[gh-action]: https://github.com/CycloneDX/gh-php-composer-generate-sbom