Add save and update pipeline trigger mutations to GraphQL

Context

This issue is a prerequisite for #42742 (closed), which will move the pipeline trigger UI to Vue. Before that can be done, the backend needs to add the ability to save and update pipeline triggers.

Proposed solution

Add mutations that allow for saving and updating pipeline triggers to GraphQL.

Queries

Get all pipelineTriggers

{
  project(fullPath: "cool-project") {
    ciCdSettings {
      pipelineTriggers {
        id
        token
        hasTokenExposed
        canAccessProject
        description
        owner
        lastUsed
      }
    }
  }
}

Mutations

Add

{
  projectPipelineTriggerAddTrigger(projectPath: $path, input: CiCdPipelineTriggerInput) {
    errors
    ...Trigger,
  }
}

Update

{
  projectPipelineTriggerUpdateTrigger(projectPath: $path, input: CiCdPipelineTriggerInput) {
    errors,
    ...Trigger,
  }
}

Delete

{
  projectPipelineTriggerRemoveTrigger(projectPath: $path, id: $id) {
    errors
    ...Trigger,
  }
}