Add autostart functionality

[BlackHoleFox]

Firstly, thank you for the great extension. I started using it with Foam and I have to say its rather nice.

I looked at the Roadmap and saw that auto start was on the list, so I thought I would give it a try. I implemented it in a pretty simple way, but it works as expected. If you start VSCode and a markdown file is currently open, it will automatically open the graph pane. If you don't have one open, but then open one at a later time after startup, it will launch the graph pane too.

To make it configurable I added an autoStart config option, defaulting to false.

And as a tiny nit (I can revert it if you want), I made the command display name more consistent with other extensions, by prefixing it with Markdown Links:

Before:

After:

[tchayen]

🤯 . Thank you so much!

Inconsistent name wasn't on purpose, it was just my lack of awareness that I am doing something wrong.