feat: Ensure we use the same default environment everywhere

[mydea]

This PR adjusts our code to use the same default environment everywhere in the codebase for consistency.
Currently, we use production some places and '' in others.

I may have missed something, but tried to find all places using this.

Closes#6239

[lforst]

We just have to be aware that this can be somewhat breaking because people may have set up alerting rules based on environment but I think this is a good change in general.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	20.12 KB (+0.07% 🔺)
@sentry/browser - ES5 CDN Bundle (minified)	62.52 KB (+0.05% 🔺)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	18.76 KB (+0.1% 🔺)
@sentry/browser - ES6 CDN Bundle (minified)	55.51 KB (+0.03% 🔺)
@sentry/browser - Webpack (gzipped + minified)	20.5 KB (+0.08% 🔺)
@sentry/browser - Webpack (minified)	66.97 KB (+0.04% 🔺)
@sentry/react - Webpack (gzipped + minified)	20.52 KB (+0.07% 🔺)
@sentry/nextjs Client - Webpack (gzipped + minified)	48.12 KB (+0.09% 🔺)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	27.09 KB (+0.08% 🔺)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	25.33 KB (+0.08% 🔺)
@sentry/replay ES6 CDN Bundle (gzipped + minified)	42.87 KB (+0.03% 🔺)
@sentry/replay - Webpack (gzipped + minified)	36.93 KB (0%)
@sentry/browser + @sentry/tracing + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	60.49 KB (+0.04% 🔺)
@sentry/browser + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	54 KB (+0.02% 🔺)

[mydea]

We just have to be aware that this can be somewhat breaking because people may have set up alerting rules based on environment but I think this is a good change in general.

Yeah, I though the same, not 100% sure, I'd tend towards is fine because it def. seems more like a bug/unexpected behavior.