* Add `Expiry` header to emails, set default expiry to 30 days and allow user config via `appsettings`
* Remove `IsSmtpExpirationConfigured` as it will always have a value
* Check for `emailExpiration` value
* Removed `EmailExpiration` default value as it should be opt-in
* Simplify SMTP email expiration condition
* Fix APICompat issue
* Add implementation to `NotImplementedEmailSender`
* Rename `emailExpiration` to `expires` to match the SMTP header
* Obsolete interfaces without `expires` parameter, delegate to an existing method.
* Set expiry TimeSpan values from user configurable settings with defaults
* Fix formating
* Handle breaking changes, add obsoletion messages and simplify interfaces.
* Fix default of invite expires timespan (was being parsed as 72 days not 72 hours).
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Co-authored-by: Andy Butland <abutland73@gmail.com>
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