define feature sets for make targets in files

[nkraetzschmar]

How to categorize this PR?

/kind enhancement
/area os
/os garden-linux

What this PR does / why we need it:

define feature sets for make targets in files, rather than having duplicate code in the Makefile and use generic make targets (% and %-dev) instead

features lists in make_targets are identical to those from the Makefile prior to this change, generated via the following script:

#!/bin/bash

set -Eeufo pipefail

makefile="$(cat Makefile)"

grep -F ': build-environment $(SECUREBOOT_CRT)' <<< "$makefile" \
| cut -d : -f 1 \
| grep -v '\-dev$' \
| while read -r target; do
	features="$(grep -F "$target"': build-environment $(SECUREBOOT_CRT)' -A 1 <<< "$makefile" \
	| tail -n 1 \
	| grep -Po '(?<=--features )[a-z0-9\-_,]+')"
	echo "$features" > "make_targets/$target"
done

[gardener-robot]

@nkraetzschmar Thank you for your contribution.

[gardener-robot]

@MrBatschner You have pull request review open invite, please check

[gyptazy]

Sorry for sliding in... Currently, I'm rewriting the garden-feat in Python where the features are being evaluated.

When building any image, the overall base is represented by a feature of the platform type. This might be e.g. KVM.

According to this PR we define these sub features (see also: https://github.com/gardenlinux/gardenlinux/pull/1259/files#diff-c2604d0d6c1ce427dd5436aae130b8cd7bf9014be12d4ec807dd8318685ec608)

target: kvm
    features:
        - server
        - cloud
        - kvm

I think we do not need to maintain these ones within the Makefiles, while this gets already done by the include features.
Given by the base kvm, it includes cloud, which includes server, that includes base and finally includes _slim.

However, by just calling the make target with kvm we get:

target: kvm
    features:
        - cloud
        - server
        - base
        - _slim

AFAIK, this should be the case for all available platforms. This works by calling garden-feat during the build time and is implemented within the currently used Go version and the upcoming Python version.

To avoid further code, it might be enough to call the platform with the desired elements and flags (if not already provided by the include chain). However, this could result in:
kvm,cis,_dev
instead of:
kvm,cloud,server,cis,_dev
with the same result.

jfyi @nanory

[nkraetzschmar]

Yes, we can definitely slim down the list of features explicitly given for each make target 👍

For this change I just wanted to keep the feature lists exactly as they were in the Makefile to ensure we don't accidentally drop any. I'd suggest we merge this as is and slim down the list of features in a separate PR to keep each change more concise.

[gardener-robot]

@nkraetzschmar You need rebase this pull request with latest master branch. Please check.