[Infra UI] Add configuration options and source graphql api

[weltenwort]

New Configuration

This PR adds new Kibana configuration options under the key xpack.infra. Any settings given in Kibana's configuration file will be overlaid on top of the following defaults (as discussed in #20428):

xpack.infra:
  sources:
    default:
      metricAlias: 'xpack-infra-default-metrics'
      logAlias: 'xpack-infra-default-logs'
      fields:
        message: ['message', '@message']
        hostname: 'beat.hostname'
        pod: 'kubernetes.pod.name'
        container: 'docker.container.name'
        timestamp: '@timestamp'
        tiebreaker: '_doc'
  query:
    partitionSize: 75
    partitionFactor: 1.2

New GraphQL Queries

Based on the configuration introduced above, the following endpoints have been added:

source(id)

extend type Query {
  "Get an infrastructure data source by id"
  source("The id of the source" id: ID!): InfraSource!
}

Example

query {
  source(id: "default") {
    id
    configuration {
      metricAlias
      logAlias
      fields {
        container
        hostname
        message
        pod
        tiebreaker
        timestamp
      }
    }
  }
}

allSources

extend type Query {
  "Get a list of all infrastructure data sources"
  allSources: [InfraSource!]!
}

Example

query {
  allSources {
    id
  }
}

Other Notes

This also distributes most of the types from infra_types.ts into the
adapter_types.ts of the respective adapters. It also moves functions and types specific to the "nodes" domain into the nodes adapter directory to increase local cohesion.

The source defaults are applied inside of the source lib instead of the configuration schema to maintain separation of concerns and because the configuration schema is Kibana-specific.

Follow-up Tasks

• move map() query type inside of source()
• use source configuration for log fetching
• add source().indices field to diagnose matching indices
• add source().capabilities field to communicate detected data characteristics

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[simianhacker]

LGTM... I tested it with GraphiQL

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