fix(core): Add sentry_client to auth headers

[lobsterkatie]

This adds sentry_client to the auth headers* we send with every envelope request, as described in the develop docs.

In order to have access to the SDK metadata, the full ClientOptions object is now passed to getEnvelopeEndpointWithUrlEncodedAuth. Despite the fact that this is really an internal function, it's exported, so in order to keep everything backwards-compatible, for the moment it will also accept a string as the second argument, as it has in the past. Finally, all of our internal uses of the function have been switched to passing options, and there's a TODO in place so that we remember to remove the backwards compatibility in v8.

Note that this change doesn't affect anyone using a tunnel, as no auth headers are sent in that case, in order to better cloak store requests from ad blockers.

*The "headers" are actually querystring values, so as not to trigger CORS issues, but the effect is the same

Fixes #5406

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	19.42 KB (+0.35% 🔺)
@sentry/browser - ES5 CDN Bundle (minified)	60.04 KB (+0.26% 🔺)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	18 KB (+0.27% 🔺)
@sentry/browser - ES6 CDN Bundle (minified)	52.94 KB (+0.26% 🔺)
@sentry/browser - Webpack (gzipped + minified)	19.76 KB (+0.28% 🔺)
@sentry/browser - Webpack (minified)	64.28 KB (+0.21% 🔺)
@sentry/react - Webpack (gzipped + minified)	19.79 KB (+0.28% 🔺)
@sentry/nextjs Client - Webpack (gzipped + minified)	44.08 KB (+0.13% 🔺)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	25.87 KB (+0.2% 🔺)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	24.12 KB (+0.23% 🔺)

[Lms24]

LGTM - Nice tests!