update community pipeline to use main branch

Problem Description: After the master branch is renamed to main, the community galaxy pipeline configuration needs to be updated to reflect the new branch name

Proposed Solution: 

1. build defaults: https://github.com/ansible/galaxy-deploy/blob/next/cicd/tekton/pipeline-galaxy-ng-build.yaml#L13
2. backend build: https://github.com/ansible/galaxy-deploy/blob/next/cicd/tekton/triggertemplate-build-ng.yaml#L17
3. frontend build: https://github.com/ansible/galaxy-deploy/blob/next/cicd/tekton/triggertemplate-build-ui.yaml#L17