chore: remove codersdk dependency

[johnstcn]

Part of https://github.com/coder/envbuilder/issues/178

In order to update our branch of Kaniko, we need to first update to go1.22. This is not currently possible while depending on codersdk.

• Manually vendored relevant parts of codersdk and agentsdk into internal/notcodersdk
• Replaced existing usage of codersdk / agentsdk with internal/notcodersdk
• Added test for coder log sending functionality

Before:

$ du -sh ./scripts/envbuilder-amd64 
64M     ./scripts/envbuilder-amd64

After:

$ du -sh ./scripts/envbuilder-amd64 
45M     ./scripts/envbuilder-amd64

[johnstcn]

Do we anticipate we will be in this state for some time?

https://github.com/coder/envbuilder/issues/193 exists to investigate removing this direct dependency. Hopefully as a result of either that or another follow-up PR we can then remove this entirely.

If so, a README in the notcodersdk would be helpful for archaeological purposes.

This is a good idea either way 👍