Add a managed dependency for `org.jvnet.mimepull:mimepull` so that
`spring-boot-starter-web-services` works with Java 11.

Although we don't directly depend on mimepull ourselves, there is an
transitive dependency from `com.sun.xml.messaging.saaj:saaj-impl:1.5.0`
which unfortunately references a version that was never published to
Maven Central.

Closes gh-14924