Add process.ai_agent.* custom documentation for Linux process events

[stanek-michal]

Register process.ai_agent.name and process.ai_agent.is_descendant in all Linux process event documentation templates that already carry the analogous process.Ext.trusted_descendant field (fork/exec/exit, already_running, gid_change, memfd_create, ptrace, shmget, uid_change).

Change Summary

Sample values

Sample document:

Release Target

Q/A

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