[Merge] ~lamoura/ubuntu/+source/base-files:update-pro-url into ubuntu/+source/base-files:ubuntu/devel

[Lucas Albuquerque Medeiros de Moura]

[Impact]
When users see the MOTD message, they are currently seeing an outdated url under the support information.
Even though the outdated url redirects to new Ubuntu Pro webpage, we believe the users should still see
the correct url from the start

[Test Case]

- Launch a LXD container for any of the affected releases
- Install the package with this fix applied
- Install `update-motd` package
- Run `update-motd` and confirm the Support url is now the correct one

[Regression Potential]
If users are parsing MOTD for some reason, the url change might break that logic now. However, parsing MOTD messages is not a supported flow, so we believe regression potential is low here.

[Discussion]
Since we want users to be aware of what Ubuntu Pro is, we should highlight the right product name on any place that is still using the old "advantage" name. Updating the support URL here is a step into this direction
-- 
https://code.launchpad.net/~lamoura/ubuntu/+source/base-files/+git/base-files/+merge/457829
Your team Ubuntu Sponsors is requested to review the proposed merge of ~lamoura/ubuntu/+source/base-files:update-pro-url into ubuntu/+source/base-files:ubuntu/devel.