Publish to Chrome and Firefox app stores

[thomaspaulb]

• Make a new signed Firefox XPI release by updating the version and using this job
• Publish to Firefox Store by uploading to Mozilla
• Add a job that autogenerates the Chrome package
• Publish to Chrome Web store by uploading to Google

[thomaspaulb]

@KKamaa To generate the XPI you'll have to fix this error in the job:

Error: InvalidManifest: Could not read manifest.json file at src/manifest.json: Error: ENOENT: no such file or directory, open 'src/manifest.json'
InvalidManifest: Could not read manifest.json file at src/manifest.json: Error: ENOENT: no such file or directory, open 'src/manifest.json'
    at getValidatedManifest (file:///home/runner/work/_actions/kewisch/action-web-ext/v1/node_modules/web-ext/lib/util/manifest.js:21:11)
    at async defaultPackageCreator (file:///home/runner/work/_actions/kewisch/action-web-ext/v1/node_modules/web-ext/lib/cmd/build.js:104:20)
    at async build (file:///home/runner/work/_actions/kewisch/action-web-ext/v1/node_modules/web-ext/lib/cmd/build.js:191:18)
    at async WebExtAction.cmd_build (file:///home/runner/work/_actions/kewisch/action-web-ext/v1/src/action.js:99:19)
    at async main (file:///home/runner/work/_actions/kewisch/action-web-ext/v1/src/index.js:59:16)

Which is probably as simple as pointing the manifest to the right folder.