Introduce "SBOM" as a new data structure in DejaCode

**Problem**
The SBOM community has identified multiple types of SBOM:
Software Bill of Materials (SBOM) -- the default of course
Software-as-a-Service Bill of Materials (SaaSBOM)
Hardware Bill of Materials (HBOM)
Machine Learning Bill of Materials (ML-BOM)
Cryptography Bill of Materials (CBOM)
Manufacturing Bill of Materials (MBOM)
Operations Bill of Materials (OBOM)

This list is ever-expanding; other variants include:
As-built SBOM
As-deployed SBOM

These various types are implemented variously by different SBOM standards (CycloneDX and SPDX).

The DejaCode Product definition is quite flexible, and Packages and Components can be defined to identify the kinds of things that exist in each SBOM type, but there is no standard way to identify the SBOM Type associated with a specific DejaCode Product, further complicated by the potential need to extract particular SBOMs of various types from the same Product Inventory.

**Benefits**
A new SBOM Type would address that need, and would support additional functionality related to various SBOM Types. Eventually this would support the generation of SBOMs from DejaCode that are more specific than the generic SBOM.

**Design Challenges**
Define SBOM Types in a new user-editable table in DejaCode?
OR
Define SBOM Types in a standard list in the source code?
OR
Do not validate SBOM Type and let it be free-form text?

Some advantages of an SBOM Type table would be:
* ability to describe exactly what the SBOM Type means to the organization
* ability to associate the SBOM Type with an SBOM Template (future ability -- this might align, for example, with SPDX SBOM "Profiles")
* ability to associate the SBOM Type with a specific SBOM Generator (program, DejaCode Report, etc. -- also future).

**Assumptions**
A DejaCode Product definition can be associated with exactly one SBOM Type in a meaningful way.