Feature: welcome/upgrade page

[AdrieanKhisbe]

With the new extension release, we need to find a way to reach our userbase to make them switch to the new publisher extension.

One way to do it, would be to publish a version that open a page explaining the user that he need to replace the extension to have latest features.
I start to dig how to implement that, (as bookmark, or gitlens do), and end up on vscode extensions samples.
So far, the current version will open the Upgrade page at start.
This is still beta and prototypal, focused on the mecanism rather than the message

Once working this would need to be backport on original extension, and a release with the original publisher should be made

We'll could later use that mecanism to publicize new features.

Feedback are more than welcome!!, I wanna know what you think about this :)

🦄

[sipi]

Sorry, @AdrieanKhisbe I did not already had the time to have a look to this PR :(
I will try to do it at the beginning of the next week.

[sipi]

Hi @AdrieanKhisbe,
thanks for this PR, I think it's the good way to reach users of the "tootone version".
Everything seems fine to me, I only made two comments to better understand some of the parts.

So, now we have to edit the message! But, I suggest we keep it simple as :

Hello Org-mode users,

please note that tootone/org-mode has become vscode-org-mode/org-mode. 
This version will probably no longer receive any update, to continue receiving 
org-mode updates please uninstall tootone/org-mode and install 
vscode-org-mode/org-mode instead.

Thank you.

We can possibly take the opportunity to add : 

We take this opportunity to remind you that org-mode is built and maintained 
by volunteers and that any help is welcome. If you like this extension and 
 have some time to devote to it, please visit the Github
repository: https://github.com/vscode-org-mode/vscode-org-mode

[AdrieanKhisbe]

Everything seems fine to me, I only made two comments to better understand some of the parts.

@sipi since it's good for you, I'll find some time to pursue this works, and incorporate your wordings :)

[sipi]

@AdrieanKhisbe feel free to reword my wording ;)