pds-solutions: remove redundancy in base image definition

[sven-dmlr]

Situation

Currently each pds solution contains an env file containing this line:

BASE_IMAGE="ghcr.io/mercedes-benz/sechub/pds-base"

This redundancy should be removed.

ToDo

• source sechub-pds-solutions/shared/environment/env-base-image in release builds before the above env file
• remove the BASE_IMAGE information from the env file of every pds-solution

[sven-dmlr]

Checked in detail and found out that in the gh-action the BASE_IMAGE variable is not taken from env file:

export BASE_IMAGE="${ACTIONS_SECHUB_REGISTRY}/pds-base:${PDS_VERSION}"

So we can safely remove the above code.

[sven-dmlr]

This issue needs more testing and probably follow-up changes. See comment https://github.com/mercedes-benz/sechub/pull/2517#pullrequestreview-1593827384

-> Somebody else can work on this issue.