Add Staging Site Deployment from CATcher repository

[seanlowjk]

Summary

This PR fixes #542

This PR is an followup to #534, which uses Github Actions to do deployment on CATcher-staging using Github Actions

Note: Please do not merge until the todos are completed!

Description

The files following play their roles in the development of the staging site at CATcher's Staging Site

Workflow Files

staging-fetch.yml enables it such that we are able to fetch CATcher-org/CATcher 's master information on push into the CATcher-org/CATcher-staging repository.

staging-deployment.yml Following which, once the master branch of CATcher-org/CATcher-staging is updated, it will activate the workflow in this file to send a build request onto github pages.

Other Files

environment.staging.ts provides the configuration for the staging site. Do note that the clientId provided by @JunWei96 helps it such that the callback URL is at https://catcher-org.github.io/CATcher-staging/

Todos

• I will force push the master branch of CATcher-staging back to be the same as CATcher so that their master branches will be even .

• I will remove cicde/staging-development from this line before merge

[seanlowjk]

Do Note: I have changed the origin on environment.prod.ts to 'https://catcher-org.github.io' in order for the authentication request to get through ><

[ptvrajsk]

LGTM 👍 Good job

[anubh-v]

Looks good, can remove the cicd/staging-deployment references so we can merge.

Another request: do add a brief comment into each workflow YAML, just stating their purpose
(for future maintainers)

[seanlowjk]

@ptvrajsk @anubh-v I have made the modifications above! Do let me know if there are any further issues!

Proposed Commit Message:

Adds two new workflow files and a staging configuration
which help to enable automatic deployment of our 
staging web application.