Previously, the JSON-B auto-configuration would be enabled when the JSON-B API was
on the classpath. This led to a failure if there was no implementation available.

The JSON-B API loads an implementation using the service loader. This commit updates
the auto-configuration to be conditional on the presence of a
META-INF/services/javax.json.bind.spi.JsonbProvider file on the classpath.

Closes gh-14675