Update the optional dependencies

[twogee]

No description provided.

[bodewig]

@twogee the switch to jakarta.mail is not backwards compatible. I don't think we can do it that way at all. Rather we'll need to introduce a new type of Mailer and an additional jar with different dependencies, I'm afraid.

[bodewig]

Thank you @twogee - do you think you could split the Jakarta Mailer support changes from the other changes?

The changes to ClasspathUtils seem to be completely unrelated to either and the chunk that removes string concatenation is completely unnecessary anyway.

[twogee]

Thanks, @bodewig, and sorry about missing the extraneous changes.
I will open a new PR for changes re Jakarta Mail specifically.
The change to ClasspathUtils is related to an attempt to avoid nested try in EmailTask#getMailerImplementation().