Add extra env vars to all components deployed with kube-thanos

[mwasilew2]

closes: https://github.com/thanos-io/kube-thanos/issues/246

• [x] I added CHANGELOG entry for this change.
• [ ] Change is not relevant to the end user.

Changes

• format the env section of kube-thanos-store.libsonnet
• add support for extraEnv (adding custom environment variables) to all kube-thanos components
• changelog entry

Verification

to test this change I edited the default values for a few components (not all!) and added the following:

          {
            name: 'JAEGER_DISABLED',
            value: 'false',
          },
          {
            name: 'JAEGER_SAMPLER_TYPE',
            value: 'probabilistic',
          },
          {
            name: 'JAEGER_SAMPLER_PARAM',
            value: '0.01',
          },
          {
            name: 'JAEGER_AGENT_HOST',
            valueFrom: {
              fieldRef: {
                fieldPath: 'status.hostIP',
              },
            },
          },

I then run make all which includes automated verification of validity of generated k8s yaml files. I also eye-balled the generated files in ./examples and ./manifests to see if they looked as expected