fix(core): update client options to allow explicit undefined

[G-Rath]

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Currently with exactOptionalPropertyTypes enabled (which is now the default for new TS projects) doing something like this is not allowed:

Sentry.init({
  dsn: process.env.SENTRY_DSN,
  environment: process.env.SENTRY_ENV ?? process.env.RAILS_ENV
});

as while undefined is supported, the types don't allow it as an explicit value.

It looks like this has come up before and Sentry is wanting to support it, though I'm not sure what ended up happening because the end ticket got closed without any associated PR.

I've purposely just opened this updating the client option properties that I think this feature is most commonly used with