Revert docs/changes relating to invalid email addresses in user feedback

[jamescrosswell]

Originally posted by @aliu39 in getsentry/sentry-docs#14103 (comment)

The behaviour to drop feedback with invalid email addresses is being reverted in Sentry:

• ref(feedback): do not validate userreport email sentry#94664

Once that's deployed we can revert both the changes to the docs and the .NET SDK. Original PRs where these changes were made:

• Describe what happens to invalid email addresses in feedback sentry-docs#14103
• Added email validation to CaptureFeedback methods #4284

[aliu39]

Perhaps we can continue validating in SDK? An invalid email won't cause any drops but an SDK error is the quickest way to let users know they've made a mistake

[jamescrosswell]

An invalid email won't cause any drops but an SDK error is the quickest way to let users know they've made a mistake

Ordinarily we wouldn't want the Sentry SDK itself to be throwing errors anywhere except when initialising the SDK.

We could, potentially, in this case make an exception to that rule since this functionality is almost certainly supported by some kind of UI experience where the application user enters some feedback and then this gets sent to Sentry.

I'm happy to follow suit with whatever the other SDKs do here.