Document the debugType context

[DanTup]

microsoft/vscode#45116 (comment)

We strongly recommend to use the when debugType context to avoid adding your actions for all debug types.

I can't find any info on debugType. I presume that it matches the currently selected debug session if there are multiple (and that it changes as you switch between the active sessions) but I think it should be written somewhere.

Also, it feels a bit weird that the place to go and find these contexts when declaring commands is to look them up in the keybinding page 🤔

[DanTup]

The text that was added isn't really as useful as it could be:

I presume that it matches the currently selected debug session if there are multiple (and that it changes as you switch between the active sessions) but I think it should be written somewhere.

debugType | True when debug type matches. Example: `"debugType == 'node'"`.

"the debug type" is a little vague since VS Code can run have multiple active debug sessions at the same time.