Add SystemRelationship support on ComponentType and ComponentTypeInput

[saditya370]

Summary

Mirrors the existing OwnerRelationship implementation 1:1 to expose the
public GraphQL systemRelationship field on ComponentType and the
corresponding argument on ComponentTypeInput.

The server-side GraphQL surface has been live for a while (monorepo MRs
!17865 / !17910), but the Go client hasn't exposed it yet. This unblocks
the Terraform provider work for OpsLevel/terraform-provider-opslevel#14687
(customer: Springer Nature).

Changes

• object.go: new SystemRelationshipType struct + SystemRelationship field on ComponentType
• input.go: new SystemRelationshipInput struct + SystemRelationship field on ComponentTypeInput
• testdata/templates/component_type.tpl: updated GraphQL query selection + mock response to include systemRelationship
• .changes/unreleased/Feature-*.yaml: changie entry

Structurally identical to OwnerRelationship — confirmed against Ruby
source definitions in the monorepo. No logic changes, no refactoring,
no new dependencies.

Test plan

• task test — full suite passes (76.9% coverage), all 5 ComponentType tests green
• task lint — clean (gofumpt + golangci-lint)
• go build ./... in terraform-provider-opslevel compiles against this branch via local replace directive

Follow-ups

• After this merges and a release is cut, bump the dependency in
  terraform-provider-opslevel and wire up the system_relationship
  attribute on the opslevel_component_type resource.
• componentTypePropagateSystemRelationship mutation is intentionally
  out of scope — it's an imperative bulk operation that doesn't map
  cleanly to declarative Terraform, and there's no precedent for it
  with owner_relationship. Can be added later if needed.