Add release checklist, cleanup version output, add release pipeline

[letmaik]

First steps towards #237.

Please have a look at this, obviously this will evolve a lot over time, but we need to get the ball rolling.

• Added a release process checklist, inspired by https://github.com/microsoft/vscode/wiki/Release-Process.
• Changed the info/version string such that both the SGX-LKL version (from VERSION file) and git commit hash is included in the binary and the command line output.
• Created a new release pipeline (and other minor CI refactoring) which can be used to release new versions to the release apt repository (as opposed to the dev apt repository that is used for all dev releases triggered by commits to oe_port).

[letmaik]

@prp @davidchisnall @paulcallen Please provide feedback and/or approve. PRs shouldn't sit idle for more than a day or two.

[hukoyu]

Looks good to me.

[letmaik]

@jxyang @Pengpeng-Microsoft Since you haven't responded I'm assuming it's all fine. It's merged in now. Please open an issue if anything should change.