* split off the Stalwart integration test boilerplate into a new
jmaptest package, in order to be able to use it from the groupware
package as well
* remove the JMAP Session patching in tests and, instead, pick random
free local ports for HTTP and IMAPS manually, and set those
explicitly in the Stalwart testcontainer, so that we can set the
PUBLIC_URL environment variable that Stalwart then uses to define the
URLs that are served as part of the JMAP Sessions (API URL, etc...)
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