Switch from Hackney to Finch as the default HTTP client

[whatyouhide]

Finch is really reliable and fast, and has significantly less dependencies than Hackney. It also exposes Telemetry events, whereas Hackney doesn't.

I think it would be nice to switch to it as the default client. We can leave Sentry.HackneyClient around for people that prefer it.

Thoughts @sl0thentr0py?

[sl0thentr0py]

yep sure if you think that's better, go for it!

[savhappy]

@whatyouhide should we have a flag that can be flipped to use Hackney instead of Finch after Finch is set as default? And apply this flag to the supervision tree upon start?

[whatyouhide]

No it's not necessary. We can just switch to Finch. If users want to use Hackney, they can write an adapter—maybe we can just put the Hackney Sentry client we have now in the codebase over into the docs if they want to copypaste that.

[savhappy]

PR out for this switch-a-roo @whatyouhide ^_^

[savhappy]

@whatyouhide alright cleaned up the deprecated errors but my mix.lock seems to be out of sync. Master and this branch currently pass locally but fail when pushed. Final blocker before another round of reviews