Support `auto_encryption` feature

.gitlab/README.md.template

README.md

src/gitlab-tofu.sh

templates/apply.yml

templates/destroy.yml

templates/full-pipeline.yml

templates/graph.yml

templates/job-templates.yml

templates/plan.yml

templates/test.yml

templates/validate-plan-apply.yml

templates/validate-plan-destroy.yml

templates/validate-plan.yml

templates/validate.yml

tests/iac/main.tf

tests/integration-tests/AutoEncryption.gitlab-ci.yml

tests/integration-tests/AutoEncryptionMigrate.gitlab-ci.yml

tests/integration-tests/WarningOnNonEmptyPlan.gitlab-ci.yml

tests/integration.gitlab-ci.yml