Implement CI MR workflow

We have one pipeline on infra-stg, one on infra-prd

1. do some change (version change, tf vars change) on some configuration(s)/envs(s)
2. create MR
3. CI run plans on all configurations/envs that are impacted by the change
   1. compute diff
   2. plan on diff
   3. store generated plans
   4. generate plan summary
4. CI report in the MR a summary of the plans
   • by adding a comment 'run plan' the CI could regenerate the plans
5. some reviewer look at the plans and validate the change by adding some comment in the MR ("run apply" for example)
6. CI detects the comment and tries to apply the plans generated earlier
   • apply last generate plans
   • if the apply succeed the MR is merged in master
   • if the apply fails, the dev should fix and update its MR (process restart at step 3.)