Add log metadata plugin

[tomasvidhall]

Tries to solve the second task in #227

2. Custom payload
Allow insertion of custom messages into each log event.

I read up on how it used to work in #267 and tried to recreate something similar to that.

Added a Log metadata plugin which can be reached using ctx.log.setMetadata() and sets the payload as metadata on the added LogEntry.

I a bit unsure about the naming of metadata, depends what you feel the terminology should be. I tried to find any mismatches and the closest I got was that there is something called action metadata for the bots, but it shouldn't collide from what I could see.

I don't usually write Typescript or Svelte, so if I missed something please point it out and I'll fix it. 🚀

Checklist

• Use a separate branch in your local repo (not master).
• Test coverage is 100% (or you have a story for why it's ok).

[tomasvidhall]

Forgot to add reviewers, labels etc and now I can't edit them, please help! 🤦

[delucis]

Hi @tomasvidhall thanks for putting this together — looks good!

There are quite a few comments in this review, so apologies if it’s a little confusing. Please ask if anything is unclear.

Basically what I’m suggesting is

1. Move metadata out of action.payload and into the top-level log entry itself.

2. Some minor tweaks to the plugin API/data.

I think the rest is mainly Typescript advice.

[tomasvidhall]

Thanks for the great review @delucis. I've updated the PR with the suggested changes. Feel free to give me more feedback.

[delucis]

Changes look good @tomasvidhall! Will run a few local tests when I’m back at my computer, but I think this looks ready to merge.