Automate publishing of release binaries

[cameel]

Extracted from #9258. Best implemented after we're done with #9932.

Currently release binaries are built on Travis and CircleCI and then manually uploaded to github release page and solc-bin. We probably don't want to automate it all the way through - we need a human in the loop to be able to verify that everything is ok and possibly intervene - but parts of this process could still be streamlined. For example the creation of a draft release and submission of a PR with binaries to solc-bin.

It will be much easier if we decide to move the builds to Github actions in #9932. The downside of doing this way is that it would not be exactly the same build that is extensively tested on CircleCI.

This was extensively discussed with @ekpyron and @chriseth in #9258 and on Gitter but we did not come to a firm decision yet. We only decided that it's not a priority and can wait until we're done with more important tasks related to the binary release process overhaul.