Add volume for home directory to the build pod

[hasanawad94]

Each container gets its own isolated emptyDir volume mounted at "/shp-writeable-home", to remove writes to the container's rootfs. Should be isolated volumes since when step 1 runs as user A but step 2 as user B, there will permission issues if this directory is shared. For Git SSH, it would actually mean that we put a private key on disk which is then unnecessarily visible

Changes

• Added logic creating and mounting a volume to be used as a home directory for the build containers.
• Mounted a volume and set HOME env value for source,build, image-processing containers.

Submitter Checklist

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

Mounting a volume to be used as a home directory for `source`,`build`, `image-processing` containers.

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[hasanawad94]

Part of #1969

[rxinui]

The changes looks clean and simple, it seems that it relies on previous changes (ie. AppendWriteableVolumes(taskSpec, &bundleStep))

Nothing to comment on, but would be better to have a second opinion.
/lgtm

[openshift-ci]

New changes are detected. LGTM label has been removed.

[hasanawad94]

@adambkaplan @SaschaSchwarze0 is it ok if we merge this ? This is one pr away from us closing #1969