Add license information for filter lists

[antonok-edm]

Storing a license field along with each of the filter list entries will allow us to easily confirm that we are allowed to ship all of the adblock lists, and will allow license information to be automatically updated in brave://adblock, preventing the two from falling out of sync with each other.

A corresponding check could be added to verify.js to ensure the field is present on all entries, and specifies a compatible license.

[MasterKia]

https://github.com/gorhill/uBlock/wiki/Filter-list-licenses

[fmarier]

Once this is generated automatically and shipped with the component, we can link to it from src/brave/components/third_paty/adblock/README.chromium (which gets pulled into brave://credits) and stop manually generating the LICENSE file from a manual copy of the metadata.