[BUG] posthog triggers and actions should use instance_url

[dannyroosevelt]

right now posthog components default to using us.posthog.com, which means EU and self-hosted customers can't use any of them. posthog.$auth now includes instance_url, which could be one of us.posthog.com, eu.posthog.com, or a custom domain in the case of self-hosted instances.

since existing auths will not have the field, we should default to us.posthog.com if that field isn't present.

[GTFalcao]

Note: this may not be as clear-cut as just replacing the base URL with the auth domain. Whoever works on this should check their documentation, there is a distinction between "public" and "private" endpoints that may have to be accounted for.

[vunguyenhung]

Hi everyone, all test cases are passed! Ready for release!

Test report
https://vunguyenhung.notion.site/BUG-posthog-triggers-and-actions-should-use-instance_url-27ebf548bb5e81a9832ff809fa7f7723