Introduce scoping for pipeline rules and mark internally generated rules as immutable.

[patrickmann]

/nocl part of ISW
/prd Graylog2/graylog-plugin-enterprise#9749

Resolves #Graylog2/graylog-plugin-enterprise/issues/9590

Introduce scoping for pipeline rules and mark internally generated routing rules as immutable. Also ensure that they cannot be added to other pipelines.
Note that these system rules are deleteable, in spite of being immutable. Until now, scoped entities needed to be mutable to be deleteable.

Motivation and Context

See linked issue

How Has This Been Tested?

Ad hoc testing and unit tests.

[patrickmann]

Frontend can distinguish internal rules returned from e.g. /api/system/pipelines/rule/paginated by evaluating the _scope field. Internal rules have the scope value of GRAYLOG_SYSTEM_PIPELINE_RULE_SCOPE e.g.:

{
"_id" : ObjectId("67ab0a63e2980a1009965461"),
"title" : "route_67ab094de2980a1009964a0a_to_Default Stream",
"description" : "Input setup wizard routing rule",
"source" : "rule "route_67ab094de2980a1009964a0a_to_Default Stream"\nwhen has_field("gl2_source_input") AND to_string($message.gl2_source_input)=="67ab094de2980a1009964a0a"\nthen\nroute_to_stream(id:"000000000000000000000001", remove_from_default: false);\nend\n",
"created_at" : ISODate("2025-02-11T08:29:23.680Z"),
"_scope" : "GRAYLOG_SYSTEM_PIPELINE_RULE_SCOPE"
}