Update CDX schema to v1.6

[sahibamittal]

Description

We currently use the CycloneDX Protobuf schema v1.4. Update the schema to v1.6: https://github.com/CycloneDX/specification/blob/master/schema/bom-1.6.proto

Addressed Issue

Closes DependencyTrack/hyades#1333

Checklist

• I have read and understand the contributing guidelines
• This PR fixes a defect, and I have provided tests to verify that the fix is effective
• This PR implements an enhancement, and I have provided tests to verify that it works as intended
• This PR introduces changes to the database model, and I have updated the migration changelog accordingly
• This PR introduces new or alters existing behavior, and I have updated the documentation accordingly

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ -0.03% (target: -1.00%)	❌ 50.00% (target: 70.00%)

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (e19cf4a)	20705	16957	81.90%
Head commit (8b49ca8)	20705 (+0)	16950 (-7)	81.86% (-0.03%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#780)	2	1	50.00%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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