feat: send test mail

[doncicuto]

Which Problems Are Solved

• Zitadel doesn't have a way to test SMTP settings either before creating a new provider or once the SMTP provider has been created.
• Zitadel SMTP messages can be more informative for usual errors

How the Problems Are Solved

• A new step is added to the new/update SMTP provider wizard that allows us to test a configuration. The result is shown in a text area.
• From the table of SMTP providers you can test your settings too.
• The email address to send the email is by default the email address for the logged in user as suggested.
• Some of the SMTP error messages have been changed to give more information about the possible situation. For example: could not contact with the SMTP server, check the port, firewall issues... instead of could not dial

Here's a video showing this new option in action:

test_smtp.mp4

Additional Changes

Replace this example text with a concise list of additional changes that this PR introduces, that are not directly solving the initial problem but are related.
For example:

• The docs explicitly describe that the property XY is mandatory
• Adds missing translations for validations.

Additional Context

• Closes SMTP send test mail #4504

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Name	Status	Preview	Comments	Updated (UTC)
docs	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jun 12, 2024 5:53pm

[doncicuto]

Hi @hifabienne, I think I've solved some issues so the review can be resumed