chore: update jenkins and plugins to latest lts, update gh actions, add flake, remove minikube and use kind (#974)

- update to latest jenkins lts
- update github actions
- add nix flake (experimental, build artifacts still wip)
- remove minikube and use kind for a better experience

variables.mk

@@ -1,4 +1,4 @@
-SHELL := /bin/bash
+SHELL := /usr/bin/env bash
 PATH  := $(GOPATH)/bin:$(PATH)
 
 OSFLAG 				:=
@@ -14,13 +14,18 @@ else
 	endif
 endif
 
-include config.base.env
+define strip_quotes
+$(shell echo $(1) | sed -e 's/^"//' -e 's/"$$//')
+endef
 
 # Import config
 # You can change the default config with `make config="config_special.env" build`
-config ?= config.minikube.env
+config ?= config.kind.env
 include $(config)
 
+include config.base.env
+$(foreach var,$(shell cat config.base.env),$(eval $(call strip_quotes,$(var))))
+
 # Set an output prefix, which is the local directory if not specified
 PREFIX?=$(shell pwd)
 
@@ -99,4 +104,4 @@ endif
 
 ENVTEST_ASSETS_DIR=$(shell pwd)/testbin
 
-PROJECT_DIR := $(shell dirname $(abspath $(lastword $(MAKEFILE_LIST))))
+PROJECT_DIR := $(shell dirname $(abspath $(lastword $(MAKEFILE_LIST))))