[FEATURE]: Add support for dependencies (`bom.dependencies`)

[madpah]

Raising here from CycloneDX/cyclonedx-python#40 given the split into this library.

CycloneDX schema version 1.2+ supports bom.dependencies which can be used to generate dependency tree graphs from CycloneDX BOMs.

This library currently has no support for bom.dependencies.

[jkowalleck]

i wrote some hints/thoughts, when i did the implementation for this feature for the PHP library.
ℹ️ this might come in handy: https://github.com/CycloneDX/cyclonedx-php-library/blob/master/docs/dev/decisions/BomDependencyDataModel.md