fix(settings): Improve mail test error handling and logging

[abhinavohri]

• Resolves: Improve error handling during email setup, when admin user didn't set a personal email yet #56609
• Closes [Bug]: Error setting up email server: AxiosError: Request failed with status code 400 #50845

Summary

This PR improves the error handling and logging when testing email settings by showing informative error message on frontend and in the server logs.

Before

After

TODO

• ...

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

[szaimen]

Tested and works!

Thanks a lot for fixing this! ☺️

[szaimen]

/backport to stable32

[szaimen]

/backport to stable31

[provokateurin]

@abhinavohri you don't need to update the branch unless there are conflicts. Please squash your commits and make sure the commit message follows https://www.conventionalcommits.org/en/v1.0.0/.

[provokateurin]

@abhinavohri you need to adjust the tests to account for the new parameter you added to the class constructor.

[welcome]

Thanks for your first pull request and welcome to the community! Feel free to keep them coming! If you are looking for issues to tackle then have a look at this selection: https://github.com/nextcloud/server/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22

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