prevent information loss on downgrade

[jkowalleck]

to prevent information loss when rendering :

• the external references should not be dropped for unknwon type. insteadd, the type should e converted to "other"

to prevent information loss when rendering CycloneDX < 1.3:

• the external references from bom.metadata should be transferred to bom

[ssonthal]

Hey @jkowalleck can i take this up if this hasn't already been addressed?

[jkowalleck]

The task is still open, and nobody is working on it.
@ssonthal , have fun working on a solution. Please follow our contribution guidelines: https://github.com/CycloneDX/cyclonedx-javascript-library/blob/main/CONTRIBUTING.md