Feat: add GitOps CLI module with complete functionalities.

[BlueLabelscotch]

Summary

Adds a new gitops module to the Harness CLI covering the five nouns from harness/cli#29.

Issue #29 verb matrix

Noun	list	get	create	update	delete	execute	Status
gitops_agent	✓	✓	✓	x	✓	✓ install	Missing update
gitops_cluster	✓	✓	✓	✓ -f	✓	—	Complete; --set deferred
gitops_repository	✓	✓	✓	✓ -f / --set	✓	—	Complete
gitops_application	✓	✓	✓	✓ -f / --set	✓	✓ sync, refresh	Complete
gitops_application_set	✓	✓	✓	✓ -f / --set	✓	—	execute:sync

What this PR adds

Module & wiring

• pkg/spec/gitops.spec.yaml — nouns, fields, 28 commands
• modules/gitops/gitops.go — execute gitops_agent:install workflow (Helm/YAML artifact fetch)
• Wired in cmd/harness/main-harness.go

CRUD (spec-only)

• Cluster / repository / application / application_set — create, update, delete with -f YAML
• ApplicationSet — scope-level API paths (/applicationset + agentIdentifier query param); server-assigned UUID
• Application — sync/refresh execute commands; delete with propagation-policy / cascade flags
• Repository — credential note in help; masked secrets excluded from --set round-trip

Update UX (--set / get-then-put)

• update gitops_repository — --set name, repo_url, type
• update gitops_application — --set target_revision, path, namespace, repo_url
• update gitops_application_set — --set name (separate get_path for GET vs PUT)
• update gitops_cluster — -f only; doc note that --set is unsupported

Engine fix

• pkg/registry/endpoint.go — apply yaml_exclude during get-then-put so read-only GET fields (e.g. status, masked password) are not sent on PUT

Test plan

• -f regression on all three update commands above
• harness create/update/delete round-trip for cluster, repository, application_set
• harness execute gitops_application:sync and :refresh
• harness execute gitops_agent:install <id> --output_file install.yaml

Closes #29