standardize graylog schema field names

[lingpri]

standardize field names in graylog common schema, will be used in codecs to map vendor specific fields.

Description

• add a constant field event_source_product.
• add 2 new fields application_sso_signonmode and application_sso_target_name
• there are 5 vendor events.action, description, severity, outcome, outcome_reason
• there are 5 non-vendor events , severity description, threat suspected, transaction type,transaction id, user type

Pending and needs clarification

Add: Where target.type = "AppInstance":

Motivation and Context

https://github.com/Graylog2/graylog-plugin-enterprise-integrations/issues/214

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.

[waab76]

One line to remove. Otherwise this looks perfect. Thanks!

[waab76]

LGTM!