Fix the smtp server password based authentication broken on realm update

[simonregn]

I don't want to get credits myself. I've copied your changes @lucdew to create this PR, so everybody can benefit from the changes you made. I didn't test it myself

[kidager]

Thank you, this is breaking smtp at every apply on 26.2

[neistow]

@kidager Any updates on this PR?

[RafaelWO]

Note that #1293 adds an option for token auth and would also set smtpServer.AuthType = "basic".

Since this existing auth type can only be basic, I tend towards simply setting it in the provider without giving the user the option to "change" it. AFAIS, this is done in #1293. I.e., if the "OAUTH" PR is accepted, it could potentially supersede this PR? 🤔