XPackPlugin created an SSLService within the plugin contructor.
This has 2 negative consequences:
1. The service may be constructed based on a partial view of settings.
Other plugins are free to add setting values via the
additionalSettings() method, but this (necessarily) happens after
plugins have been constructed.
2. Any exceptions thrown during the plugin construction are handled
differently than exceptions thrown during "createComponents".
Since SSL configurations exceptions are relatively common, it is
far preferable for them to be thrown and handled as part of the
createComponents flow.
This commit moves the creation of the SSLService to
XPackPlugin.createComponents, and alters the sequence of some other
steps to accommodate this change.
Backport of: #49667
cad0f6bf28