fix output sbom schema

[viveksahu26]

closes #328

This PR adds the following changes:

• correct schema as per provided --outputSpecVersion
• Added integration test for the same.

Example:

$ go run main.go assemble --augmentMerge --primary  samples/test/assemble/lite-sbom1-cdx.json samples/test/assemble/lite-sbom2-cdx.json -o augment-Merge-default-default-version.cdx-new.json

$ go run main.go assemble --augmentMerge --primary  samples/test/assemble/lite-sbom1-cdx.json samples/test/assemble/lite-sbom2-cdx.json -o augment-Merge-default-16.cdx-new.json --outputSpecVersion=1.6

$ go run main.go assemble --augmentMerge --primary  samples/test/assemble/lite-sbom1-cdx.json samples/test/assemble/lite-sbom2-cdx.json -o augment-Merge-default-15.cdx-new.json --outputSpecVersion=1.5

$ go run main.go assemble --augmentMerge --primary  samples/test/assemble/lite-sbom1-cdx.json samples/test/assemble/lite-sbom2-cdx.json -o augment-Merge-default-14.cdx-new.json --outputSpecVersion=1.4

Now validate schema using sbomqs:

$ sbomqs score -f sbom_schema_valid augment-Merge-default-default-version.cdx-new.json
Feature Quality Score: 10.0/10.0     Grade: A    Components: 6      EngineVersion: 8    File: augment-Merge-default-default-version.cdx-new.json

Feature Breakdown:
+-------------------+-----------+-------+----------+
|      FEATURE      |   SCORE   | GRADE |   DESC   |
+-------------------+-----------+-------+----------+
| sbom_schema_valid | 10.0/10.0 | A     | complete |
+-------------------+-----------+-------+----------+

$ sbomqs score -f sbom_schema_valid augment-Merge-default-16.cdx-new.json             
Feature Quality Score: 10.0/10.0     Grade: A    Components: 6      EngineVersion: 8    File: augment-Merge-default-16.cdx-new.json

Feature Breakdown:
+-------------------+-----------+-------+----------+
|      FEATURE      |   SCORE   | GRADE |   DESC   |
+-------------------+-----------+-------+----------+
| sbom_schema_valid | 10.0/10.0 | A     | complete |
+-------------------+-----------+-------+----------+

$ sbomqs score -f sbom_schema_valid augment-Merge-default-15.cdx-new.json
Feature Quality Score: 10.0/10.0     Grade: A    Components: 6      EngineVersion: 8    File: augment-Merge-default-15.cdx-new.json

Feature Breakdown:
+-------------------+-----------+-------+----------+
|      FEATURE      |   SCORE   | GRADE |   DESC   |
+-------------------+-----------+-------+----------+
| sbom_schema_valid | 10.0/10.0 | A     | complete |
+-------------------+-----------+-------+----------+

$ sbomqs score -f sbom_schema_valid augment-Merge-default-14.cdx-new.json
Feature Quality Score: 10.0/10.0     Grade: A    Components: 6      EngineVersion: 8    File: augment-Merge-default-14.cdx-new.json

Feature Breakdown:
+-------------------+-----------+-------+----------+
|      FEATURE      |   SCORE   | GRADE |   DESC   |
+-------------------+-----------+-------+----------+
| sbom_schema_valid | 10.0/10.0 | A     | complete |
+-------------------+-----------+-------+----------+