Refactor rover apply to reuse an existing terraform plan

At the moment the rover apply is running a terraform plan and apply behind the scene. This issue fix that and propose the following:

if no plan is provided then rover apply will execute rover plan and apply
If a plan is provided as a parameter rover apply will use that plan instead of creating a new one

The scenario we want to cover are

Run rover plan in cd pipelines and store the plan in an artifact repo
Perform a review
Execute the apply based on the plan stored in the artifact

Commands to separate plan from apply and destroy.

Plan for an apply

# Rover plan for an apply
rover \
  -lz /tf/caf/landingzones/caf_launchpad \
  -var-folder /tf/caf/configuration/contoso/platform/demo/level0/launchpad \
  -tfstate_subscription_id ${tfstate_subscription_id} \
  -target_subscription ${target_subscription} \
  -tfstate caf_launchpad.tfstate \
  -log-severity ERROR \
  -launchpad \
  -env it-sre \
  -level level0 \
  -p ${TF_DATA_DIR}/tf_plan_launchpad.tfplan \
  -a plan

# Rover apply based on the previous plan
rover \
  -lz /tf/caf/landingzones/caf_launchpad \
  -var-folder /tf/caf/configuration/contoso/platform/demo/level0/launchpad \
  -tfstate_subscription_id ${tfstate_subscription_id} \
  -target_subscription ${target_subscription} \
  -tfstate caf_launchpad.tfstate \
  -log-severity ERROR \
  -launchpad \
  -env it-sre \
  -level level0 \
  -p ${TF_DATA_DIR}/tf_plan_launchpad.tfplan \
  -a apply

Plan for a destroy

# Rover plan for a destroy
rover \
  -lz /tf/caf/landingzones/caf_launchpad \
  -var-folder /tf/caf/configuration/contoso/platform/demo/level0/launchpad \
  -tfstate_subscription_id ${tfstate_subscription_id} \
  -target_subscription ${target_subscription} \
  -tfstate caf_launchpad.tfstate \
  -log-severity ERROR \
  -launchpad \
  -env it-sre \
  -level level0 \
  -p ${TF_DATA_DIR}/tf_plan_launchpad.tfplan \
  -a plan -destroy

# Rover destroy based on the previous plan. Note -var-folder, -var-file or -var must be removed from the command line.
# As the destroy is now based on the plan, terraform is not prompting for the confirmation to destroy the resources
rover \
  -lz /tf/caf/landingzones/caf_launchpad \
  -tfstate_subscription_id ${tfstate_subscription_id} \
  -target_subscription ${target_subscription} \
  -tfstate caf_launchpad.tfstate \
  -log-severity ERROR \
  -launchpad \
  -env it-sre \
  -level level0 \
  -p ${TF_DATA_DIR}/tf_plan_launchpad.tfplan \
  -a destroy

Previous commands are still working

# Rover plan
rover \
  -lz /tf/caf/landingzones/caf_launchpad \
  -var-folder /tf/caf/configuration/contoso/platform/demo/level0/launchpad \
  -tfstate_subscription_id ${tfstate_subscription_id} \
  -target_subscription ${target_subscription} \
  -tfstate caf_launchpad.tfstate \
  -log-severity ERROR \
  -launchpad \
  -env it-sre \
  -level level0 \
  -a plan

# Rover apply
rover \
  -lz /tf/caf/landingzones/caf_launchpad \
  -var-folder /tf/caf/configuration/contoso/platform/demo/level0/launchpad \
  -tfstate_subscription_id ${tfstate_subscription_id} \
  -target_subscription ${target_subscription} \
  -tfstate caf_launchpad.tfstate \
  -log-severity ERROR \
  -launchpad \
  -env it-sre \
  -level level0 \
  -a apply

# Rover destroy
rover \
  -lz /tf/caf/landingzones/caf_launchpad \
  -var-folder /tf/caf/configuration/contoso/platform/demo/level0/launchpad \
  -tfstate_subscription_id ${tfstate_subscription_id} \
  -target_subscription ${target_subscription} \
  -tfstate caf_launchpad.tfstate \
  -log-severity ERROR \
  -launchpad \
  -env it-sre \
  -level level0 \
  -a destroy

aztfmod / rover

Refactor rover apply to reuse an existing terraform plan #165