Issue-1306: Make Email Activity event class and email object more generic

[Aniak5]

Related Issue:

#1306

Description of changes:

• Add protocol_name and command to email activity event class
• Addto_mailboxes/from_mailbox/cc_mailboxes/delivered_to_list/reply_to_mailboxes to email object
• Deprecate smpt_to/smtp_from/smtp_hello/delivered_to/reply_to
• Update banner description to be more generic

[Aniak5]

@JW-Corelight, @zschmerber @mikeradka do we want to add similar *_details fields for reply_to and delivered_to?

[JW-Corelight]

It looks like you're right that both reply_to and delivered_to have the same issue - they can contain both the display name and the routable email address, so it make sense for them to have the *_details fields as well

[pagbabian-splunk]

Minor point - for message_uid we should also use the Source meta data keyword for "Message-ID"

[floydtree]

There is a breaking change (hardening requirement of activity_id) in this PR that the community collectively agreed to pass through. All 3 Email Activity * star classes had a bug since v1.0.0, where it had overwritten activity_id's requirement from required to optional in its definition.

This directly conflicts with usage of activity_id throughout the framework, as it is one of the primary classifiers in all event classes and is expected to be populated in all OCSF events. The has community collectively agreed to fix this within the v1 major cycle, even though this can technically be classified as a breaking change considering it as a critical bugfix.

@pagbabian-splunk @Aniak5 @mikeradka @jasonbreimer