Backend: Support inputs for triggers

Summary

As a part of Add support for spec:inputs in GitLab CI pipelines (&16321 - closed); support inputs for trigger

• Accept inputs in trigger:include for parent-child pipelines:

child-pipeline:
  trigger:
    include: 'child.gitlab.ci.yml'
    inputs: 
        security_scan: true
        level: 20

• Accept trigger:inputs for multi-project pipelines"

multi-project-pipeline:
  trigger: 
    project: group/project
    inputs: 
        security_scan: true
        level: 20

NOTES:

• Ensure execute_params has inputs included
• Ensure that trigger:inputs and trigger:include:inputs are mutually exclusive.