Exclude NULLs from component hash indexes

[nscuro]

Description

Excludes NULLs from component hash indexes.

Component hashes are only queried via the component search. This implicates that parameters to those queries are never NULL.

We never sort by hashes since that would be pointless.

Chances are extremely high that not all hash types will be populated for any given component.

There is thus no benefit to indexing NULL values. Excluding NULLs will keep indexes sizes smaller, and make index updates faster, while still allowing for performant lookups.

Addressed Issue

Closes DependencyTrack/hyades#1642

Additional Details

N/A

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
✅ +0.00% (target: -1.00%)	✅ ∅ (target: 70.00%)

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (a8a454a)	22285	18477	82.91%
Head commit (e206405)	22285 (+0)	18477 (+0)	82.91% (+0.00%)

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Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#1037)	0	0	∅ (not applicable)

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