Initial support for 2021.3 Alerts, some housekeeping

[nblumhardt]

Since there's quite a bit more information we can add to the 2021.3 alerts, to keep the size of the PR manageable and to make things reviewable, I thought I'd send this checkpoint PR first

This PR:

• Pulls some of the Seq event recognition/handling logic out into its own class
• Adds a test project and some tests for the above
• Moves as much initialization as possible to the OnAttached() hook
• Adds Run.ps1, which will use seqcli (if installed) to run the app outside of Seq (avoiding packaging/app installation etc. for debugging 🎉 )
• Sets the correct "open" URL for 2021.3 alerts, when they're encountered
• Attempts to fix some inconsistent whitespace

There's one small functional change: the code only includes the (potentially sensitive?) Teams webhook URL in diagnostic events when the TraceMessage flag is enabled, and adds a warning about this to the help text for that property. My reasoning is that it's not otherwise apparent that the webhook URL will end up in Seq events when errors occur (thoughts?).

Still works as before, on my local instance:

I tried to follow the project's style/conventions as much as possible, but I'm not 100% sure of the intention in all places, so if there's anything you'd like tweaked or reverted no matter how trivial, as always, please just let me know :-)

[MattMofDoom]

I was looking at updating the Teams app to include AdaptiveCards, but, uh .. yeah, not fabulous after my initial pass. The adaptive cards story is a bit of a mess tbh. Will be awesome to see the 2021.3 update take shape here - we use it a lot.

[AntoineGa]

it looks good to me. Why are we removing ForContext in log though ?

[AntoineGa]

ok, re-reading, it's fine. It takes some times to get the GetProperty loop, just by reading it