Prepare pre-release workflow

[Adam-it]

Currently when we want to perform a pre-release we need to manually pull latest dev and manually bump the patch version in package.json and shrinkwrap and commit it to the repo.

If we are in a hurry it is almost impossible to do that over the phone, also mistakes happen and it's normal, if we would automate this we could prevent mistakes in future.

The idea is to add a new workflow that would bump the patch version for us on dev branch and would open a PR for us that targets dev branch and with title like "pre-release vx.y.z"
That way we may just quickly recheck on the PR if the modified files are correct, and merge like any other PR.
After that we may just start the pre-release workflow as we do now.

That way we would reduce the amount of manual code we need to write to perform a pre-release and reduce the mistakes that may happen along the way.

Instead the pre-release flow would be just:

1. Run the prepare pre-release flow that does the bump and opens a PR
2. Quick check on the PR and merge
3. Run the pre-release flow that does the publish on the marketplace

[Adam-it]

In an other extension I maintain I have a similar flow that does a bit more but also runs a PowerShell script which performs the version bump as well
https://github.com/pnp/vscode-pnp-powershell/blob/main/.github%2Fworkflows%2Fprepare-release.yml

We could do something similar

[Saurabh7019]

Let's do it. I made a mistake recently and with automation we could avoid similar mistakes.

[Adam-it]

Let's do it. I made a mistake recently and with automation we could avoid similar mistakes.

Awesome, let's mark ship it then but I would like not to open it up for other contributors.
I feel that maintaining repo workflows should rather be developed by maintainers to avoid any unwanted behaviors