feat: github actions to build browser extension for pull requests

[aatmanvaidya]

Describe the PR
This PR resolves #347.
This PR has the github action code to build the browser extension when a pull request is made to the main branch of tattle-made/Uli.
Once a user makes the PR, a comment (bot) will pop up having 2 links. One which contains the build folder for firefox and the other for chrome.

Steps to test the PR

1. Make a pull request to the main branch of tattle-made/Uli

@dennyabrain apologies for the large number of commits, but every time to test a change in the action, I had to push the changes and make a PR to test them out.

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[dennyabrain]

No worries about the multiple commits. Unfortunately there's no other way to test github actions, so this was expected :) i'll squash them into one commit so not a problem.

Lets see if we can combine the two actions into 1. I think we could build the firefox and chrome version in the same action. So the build action could look something like

cd browser-extension/plugin
ls
pwd
npm install
npm run build:firefox
mv dist/ extension-firefox/
npm run build
mv dist/ extension-chrome/

Then configure the upload-artifact action :

- uses: actions/upload-artifact@v3
  with:
    name: my-artifact
    path: |
      dist-firefox/
      dist-chrome/

I think this would create one artifact zip files with two folders for each extension.

[aatmanvaidya]

I think the github actions are failing because we haven't given write access for GITHUB_TOKEN. We will have to do that in tattle-made/Uli