feat: Disable relay by default in devservices

[dcramer]

Requires getsentry/sentry#32497

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[dcramer]

Aside you'll note I moved Env to the top of our dev docs, because generally it is the first and largest complexity a contributor needs to tackle. There are some areas that could use improvement elsewhere, like the 'Workflow' page which feels very out of place now and misaligned with other pages.