Make required field determine whether the parameter is required

What type of PR is this?

/kind optimization /area devops

What this PR does / why we need it:

Make required field decide whether the form item is required.

We have decided to add a required field to determine whether the parameter is required to input instead of using default field. See

• https://github.com/kubesphere/ks-devops/pull/489

for more.

Which issue(s) this PR fixes:

Fixes #

Special notes for reviewers:

Steps to test:

1. Apply a ClusterTemplate for test:

   cat <<'EOF' | kubectl apply -f -
   apiVersion: devops.kubesphere.io/v1alpha3
   kind: ClusterTemplate
   metadata:
     name: echo
   spec:
     parameters:
     - default: John
       name: 姓
       required: false
     - default: Niang
       name: 名
       required: true
     template: |
       pipeline {
         agent none
         stages {
           stage('echo') {
             steps {
               echo 'Hello, $(.params.姓)-$(.params.名)!'
             }
           }
         }
       }
   EOF

2. Create a Pipeline for test
3. Edit Pipeline and select the ClusterTemplate created just now
4. See the result

Does this PR introduced a user-facing change?

None

Additional documentation, usage docs, etc.: