Add volume for trivy

[hasanawad94]

Breaking the changes of #1885 into smaller prs to make review easier in the effort of better security practices for the containers that are used for the build process.

Changes

Added env variables for trivy to configure writing to volumes instead of the root filesystem.
Added a utility function AppendWriteableVolumes to be used for appending volumes to steps.

Volumes introduced to trivy:

• volume for trivy cache
• volume for tmp data

Set env variables:

• TRIVY_CACHE_DIR
• TMPDIR

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• Includes tests if functionality changed/was added
• Includes docs if changes are user-facing
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Release Notes

Added volumes and config for trivy to enable its cache and tmp data to be on a volume instead of root filesystem.

[hasanawad94]

/release-note

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[rxinui]

One possible improvement otherwise it lgtm.

[adambkaplan]

Documenting the "bigger picture" request here: #1969

[hasanawad94]

@rxinui , @adambkaplan looks OK and safe to merge ?

[rxinui]

/lgtm

[SaschaSchwarze0]

/approve
/lgtm

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