feat: add custom env to logical backup

[farodin91]

fixes #1473

codegen failed with

./hack/update-codegen.sh                                  
Generating deepcopy funcs
Generating clientset for acid.zalan.do:v1 zalando.org:v1 at github.com/zalando/postgres-operator/pkg/generated/clientset
Generating listers for acid.zalan.do:v1 zalando.org:v1 at github.com/zalando/postgres-operator/pkg/generated/listers
Generating informers for acid.zalan.do:v1 zalando.org:v1 at github.com/zalando/postgres-operator/pkg/generated/informers
cp: cannot stat 'github.com/zalando/postgres-operator/pkg/*': No such file or directory

[FxKu]

Since we merged #2051 this PR seems to be obsolete. I hope you don't mind if I close it. We might think of passing env variables from the cluster manifest to the logical backup pod, too. But I don't really like to have an EnvVar section for logical backup in the Postgresql manifest itself.