fix: Make extension using Manifest V3 compatible with Firefox

[bee344]

This PR's goal is to make the extension compatible with Firefox, while still being compatible with the new Manifest V3 introduced on #1367 .

Changes

• Now there are two manifests: manifest_firefox.json and manifest_chrome.json, with each containing the configuration for each browser. There's also a dummy manifest.json which contents are modified depending on what's the target build. This is set like this to avoid the risk of getting an error in the build after modifying the name of the file and getting stuck. This way if the build is cut short, the only thing that changes is the content of the dummy manifest.
• The target .zip files names were updated to reflect the new targets: master-<TARGET_BROWSER>-build.zip and master-<TARGET_BROWSER>-src.zip.
• The build and build:zip were updated to run the specific build scripts that were added for each target, in order to not break the CI, but now we can also build just the assets specific for the target browser we want or for both.
• Updated README.md

[TarikGul]

GH_RELEASE_FILES in CI needs to be updated :)

[ryanleecode]

running yarn build updates the packages/extension/manifest.json to "service_worker": "background.js",

[ryanleecode]

Ah nvm thats intended

[TarikGul]

yea yarn build is mainly intended for the CI, for browser specific builds run yarn build:ff or yarn build:chrome

[polkadot-js-bot]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.