rel: prep v0.4.0b0 release

[brookesargent]

Which problem is this PR solving?

Prep the 0.4.0 release (wasn't totally sure if this should be a or b)

[VinozzZ]

I'm curious as well about whether this should be a prepatch(b) or prerelease(a) @JamieDanielson

[JamieDanielson]

🤔 Hm. The versioning in prereleases of python seem to be a bit funky, and this tool we use for poetry version doesn't seem to work well with our suffixes. We think we should've had 0.3.0b0 as our previous release, which would mean a beta instead of alpha, similar to how upstream otel-python appears to version their beta/experimental packages.

So let's make this v0.4.0b0.

[JamieDanielson]

I'll update the releasing doc to remove that versioning section in a follow-up PR.

[brookesargent]

🤔 Hm. The versioning in prereleases of python seem to be a bit funky, and this tool we use for poetry version doesn't seem to work well with our suffixes. We think we should've had 0.3.0b0 as our previous release, which would mean a beta instead of alpha, similar to how upstream otel-python appears to version their beta/experimental packages.

So let's make this v0.4.0b0.

Thanks for looking into it! Done!

Updated version number as requested