ci: 🎡 create terraform plan summary and post as comment to pr

[jaskaransarkaria]

ported code from this github action

Comments look like this:

• output terraform plan to file
• read tfplan and generate a summary
• summary unit tests
• post summary to pr as a comment

closes https://github.com/ministryofjustice/cloud-platform/issues/5995

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 38.70968% with 95 lines in your changes missing coverage. Please review.

Project coverage is 37.83%. Comparing base (a94794e) to head (820cc4c). Report is 51 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/environment/mocks/Applier.go	0.00%	25 Missing and 4 partials :warning:
pkg/mocks/terraform/terraformExec.go	0.00%	10 Missing and 9 partials :warning:
pkg/environment/applier.go	0.00%	17 Missing :warning:
pkg/github/client.go	0.00%	14 Missing :warning:
pkg/environment/environmentApply.go	0.00%	10 Missing :warning:
pkg/environment/createPlanSummary.go	90.90%	6 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #636 +/- ## ========================================== + Coverage 37.11% 37.83% +0.71% ========================================== Files 50 74 +24 Lines 3225 4924 +1699 ========================================== + Hits 1197 1863 +666 - Misses 1903 2854 +951 - Partials 125 207 +82 ```

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