Enable leader election for controller manager

[khos2ow]

Description of your changes

This PR enables leader election for Alibaba provider controller manager. This can be controlled by --leader-election CLI flag or LEADER_ELECTION=true environment variables. This can be achieved for deployment by applying the following:

apiVersion: pkg.crossplane.io/v1alpha1
kind: ControllerConfig
metadata:
  name: alibaba-config
spec:
  replicas: 2
  env:
    - name: "LEADER_ELECTION"
      value: "true"

Partial fix for https://github.com/crossplane/crossplane/issues/5

I have:

• [x] Read and followed Crossplane's contribution process.
• [x] Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

TBA