Use spdx/tools-golang rather than internal spdx.go file

[nishakm]

Upstream spdx tools already define structs which reflect the data model for each version of the specification. Rather than duplicate work, use the upstream models.

[ba11b0y]

Is this up for grabs? If yes, I'd like to work on this as my first contribution here!

[ba11b0y]

From what I could understand was, instead of defining Relationship here

spdx-sbom-generator/pkg/models/spdx.go

Line 53 in f702b30

type Relationship struct {

A better idea is to import tools-golang and directly refer to https://github.com/spdx/tools-golang/blob/main/spdx/v2/v2_3/relationship.go#L10

Is this the right approach to follow for all others?