Reduce memory usage of metrics update tasks

[nscuro]

Description

Reduces memory usage of metrics update tasks.

Because the tasks iterated over large datasets (i.e. all projects, or all components of a project), the DataNucleus L1 cache kept growing. Prevent this from happening by evicting objects from the cache after every iteration.

Also, because setting a FetchGroup on Query level doesn't overwrite the FetchGroup on PersistenceManager level, too many fields were being loaded. Use ScopedCustomization to overwrite the PM's FetchGroup when querying objects for metrics calculation.

Addressed Issue

N/A

Additional Details

Based on the fixes for repository meta analysis introduced in #4311.

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 added corresponding update logic
• 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%)	✅ 100.00% (target: 70.00%)

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (687e997)	22537	17832	79.12%
Head commit (0d55a88)	22551 (+14)	17843 (+11)	79.12% (+0.00%)

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 (#4325)	36	36	100.00%

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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