fix: Safeguard for Sentry default templates + nitpick

[HazAT]

Hey,
I added a small safeguard to not break the frontend once a user added Sentry.
process is undefined if a user doesn't add it to redwood.toml, and it results in the default rendering a blank page.
Before

This fix adds a safeguard and some barebone instructions on what a user has to do.
After

• Also added a fix for @sentry/tracing imports; We recently deprecated the need to import it from there separately
• Changed the default value of the DSN from https://[email protected]/XXXXXXX to '' (empty string) because the other one might result in an error
• Add HTTP Tracing integration to continue the trace from the frontend

[jtoar]

Hey @HazAT, yeah we could do with a better error, the "process is undefined" one leaves a lot to be desired. Left a comment on the conditional, let me know what you think. Thanks!

[jtoar]

The way Vite works (on Redwood v6), it replaces whole "property access" chains (I'm not sure what the word is), like process.env.SENTRY_DSN. The process object doesn't really exist. So I think process will always be undefined. Anyway, the upshot is that it's probably better to just check the second one:

Suggested change

	if (typeof process === 'undefined' || !process.env.SENTRY_DSN) {
	if (!process.env.SENTRY_DSN) {

[HazAT]

I tried it just with just the second condition but it still throws Uncaught ReferenceError: process is not defined
tbf I only tested in dev and not a prod build.

[Tobbe]

Thanks again for your PR @HazAT 🙏 Sorry it got stuck 🙁

A couple of the changes were addressed in this recent PR: #9542 But other changes here are still valuable! I'll see what I can do about getting this merged.