Move constrain to only have a single command in backend to run to dedicated backends (#1032)

at the moment we compile a script that we can pipe in as single command
this is because of the constrains the docker backend gives us.

so we move it into the docker backend and eventually get rid of it altogether

pipeline/backend/kubernetes/pod.go

@@ -3,6 +3,7 @@ package kubernetes
 import (
 	"strings"
 
+	"github.com/woodpecker-ci/woodpecker/pipeline/backend/common"
 	"github.com/woodpecker-ci/woodpecker/pipeline/backend/types"
 	v1 "k8s.io/api/core/v1"
 	"k8s.io/apimachinery/pkg/api/resource"
@@ -10,8 +11,13 @@ import (
 )
 
 func Pod(namespace string, step *types.Step) *v1.Pod {
-	var vols []v1.Volume
-	var volMounts []v1.VolumeMount
+	var (
+		vols       []v1.Volume
+		volMounts  []v1.VolumeMount
+		entrypoint []string
+		args       []string
+	)
+
 	if step.WorkingDir != "" {
 		for _, vol := range step.Volumes {
 			vols = append(vols, v1.Volume{
@@ -36,13 +42,13 @@ func Pod(namespace string, step *types.Step) *v1.Pod {
 		pullPolicy = v1.PullAlways
 	}
 
-	command := step.Entrypoint
-	args := step.Command
-	envs := mapToEnvVars(step.Environment)
-
-	if _, hasScript := step.Environment["CI_SCRIPT"]; !strings.HasSuffix(step.Name, "_clone") && hasScript {
-		command = []string{"/bin/sh", "-c"}
-		args = []string{"echo $CI_SCRIPT | base64 -d | /bin/sh -e"}
+	if len(step.Commands) != 0 {
+		scriptEnv, entry, cmds := common.GenerateContainerConf(step.Commands)
+		for k, v := range scriptEnv {
+			step.Environment[k] = v
+		}
+		entrypoint = entry
+		args = cmds
 	}
 
 	hostAliases := []v1.HostAlias{}
@@ -97,10 +103,10 @@ func Pod(namespace string, step *types.Step) *v1.Pod {
 				Name:            podName(step),
 				Image:           step.Image,
 				ImagePullPolicy: pullPolicy,
-				Command:         command,
+				Command:         entrypoint,
 				Args:            args,
 				WorkingDir:      step.WorkingDir,
-				Env:             envs,
+				Env:             mapToEnvVars(step.Environment),
 				VolumeMounts:    volMounts,
 				Resources:       resources,
 				SecurityContext: &v1.SecurityContext{