fix(nextjs): Add env var to suppress API non-response meta-warning

[lobsterkatie]

In the nextjs SDK, when we wrap users' API routes, we also wrap the response's end method, in order to keep the lambda running the route handler alive long enough to send events to Sentry. As a consequence, however, Next thinks a response hasn't been sent at all, because end hasn't been called within the timeframe that it expects, so it throws a warning in dev.

A previous attempt to fix this problem backfired, and had to be reverted, so as a compromise option for the moment, we log a warning about the Next warning, so at least people know it's nothing to worry about. Some people are finding this behavior spammy, though, so this PR adds an env variable check which allows a user to suppress our meta-warning, and also improves the warning itself so that people know the option is there.

[github-actions]

size-limit report

Path	Base Size (ba14cc5)	Current Size	Change
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	20.43 KB	20.43 KB	+0.01% 🔺
@sentry/browser - ES5 CDN Bundle (minified)	65.2 KB	65.2 KB	0%
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	19.01 KB	19.01 KB	+0.01% 🔺
@sentry/browser - ES6 CDN Bundle (minified)	58.22 KB	58.22 KB	0%
@sentry/browser - Webpack (gzipped + minified)	22.3 KB	22.3 KB	0%
@sentry/browser - Webpack (minified)	76.58 KB	76.58 KB	0%
@sentry/react - Webpack (gzipped + minified)	22.33 KB	22.33 KB	0%
@sentry/nextjs Client - Webpack (gzipped + minified)	46.56 KB	46.56 KB	0%
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	27.25 KB	27.25 KB	+0.01% 🔺
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	25.62 KB	25.62 KB	0%

[Lms24]

Looks good to me (aside from the linter errors obviously).

[lobsterkatie]

Looks good to me (aside from the linter errors obviously).

Damn, I wonder why VSCode didn't catch that. 🤔 Anyway, fixed.