Add new policy fields for firewall_anti_tamper plugin

[matthewh-elastic]

Change Summary

Add additional Policy field entries for new firewall_anti_tamper plugin.

For mapping changes:

• I ran make after making the schema changes, and committed all changes
• If these field(s) are "exception"-able, I made a companion PR to Kibana adding it (see Readme)
• If this is a metadata change, I also updated both transform destination schemas to match

For Transform changes:

• The new transform successfully starts in Kibana
• The corresponding transform destination schema was updated if necessary

[intxgo]

the descriptions doesn't look good

[pzl]

Can you please add sample values for these new fields to package/endpoint/data_stream/policy/sample_event.json?

[brian-mckinney]

You could also add the example field to these definitions. It's useful for enhancing the auto generated docs (see: #606)

[matthewh-elastic]

Thanks. All of the fields for existing plugins are currently in the same format (eg here) so I copied these for consistency. Perhaps a separate PR could be raised to add the example field to all of them at once?