Inject MailSession with CDI Inject

Like other resource definition, such the resource definition and injections in Concurrency.

1. Inject default `Mail Session` via CDI `@Inject`.
2. add a qualifier attribute to `MailSessionDefiction` to accept a custom CDI `@Qualifier`
3. Make the attributes of `MailSessionDefiction` accept Expression Language.

Start by reviewing the existing resource definitions and injections in Concurrency, then locate the MailSessionDefiction API and its current attributes. Define the required CDI injection, qualifier support, and Expression Language behavior before identifying the specification tests or examples that must be updated; done means all three requested capabilities are specified and covered.

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