publish pre-release versions to the marketplaces

[GitMensch]

Is your feature request related to a problem?
So far preview versions can only be installed manually from vsix.

Describe the solution you'd like
Publish pre-release versions of the extension.

Additional information
https://code.visualstudio.com/api/working-with-extensions/publishing-extension#prerelease-extensions

[ishche]

I like this idea!
We could have continuous delivery into prerelease versions of extensions.

[Nurkambay]

Good idea!

[slavek-kucera]

Excellent idea, except I've just run into microsoft/vsmarketplace#310

[GitMensch]

As noted in the referenced issue and in the docs: increment the minor version (possibly directly after a release), push all the preview/rc versions to the marketplace with an incrementing patch version and when preview is over set the patch to zero and increment the minor version. This way an "odd" minor number will always be a stable-release, while an even number is used for pre-releases.