Feature request: Add methods to check for sender and recipient(s)

For the upcoming feature to look for the nth message, I propose a new
feature request (will provide a PR):
- add method `seeSenderInLastEmail`/`seeSenderInNthEmail` to check for the correct sender
- add method `seeRecipientInLastEmail`/`seeRecipientInNthEmail` to check for certain recipient(s)

The data is there and could easily be integrated in the `\Codeception\Util\Email` entity and `\Codeception\Module\MailCatcher` module.

Start by reading the Codeception\Util\Email entity and Codeception\Module\MailCatcher module named in the issue, then trace how the existing last- and nth-email lookup works. Done means sender and recipient checks are available for both the last email and a selected nth email, including recipient(s) as requested.

由索引模型根据 Issue 内容生成。