Add Dagster exporter to list of miscellaneous exporters

[HirofumiTsuda]

Adds the Dagster exporter to the Miscellaneous section, in alphabetical order (between c-lightning exporter and DHCPD leases exporter).

It polls Dagster's GraphQL API directly and exposes run-state metrics (active runs, completed runs, latest run status) as Prometheus metrics, avoiding the blind spots of Dagster's official Pushgateway-based integration (e.g. crashed/queued runs that never get a chance to push).

Sample output:

dagster_active_runs{job_name="heavy_job",location="dev-dagster-workspace",status="queued"} 0
dagster_active_runs{job_name="heavy_job",location="dev-dagster-workspace",status="started"} 1
dagster_active_runs{job_name="heavy_job",location="dev-dagster-workspace",status="starting"} 0

dagster_completed_runs_total{job_name="heavy_job",location="dev-dagster-workspace",status="failure"} 0
dagster_completed_runs_total{job_name="heavy_job",location="dev-dagster-workspace",status="success"} 12
dagster_completed_runs_total{job_name="failing_job",location="dev-dagster-workspace",status="failure"} 3

dagster_last_run_info{job_name="heavy_job",location="dev-dagster-workspace",status="success"} 1
dagster_last_run_info{job_name="failing_job",location="dev-dagster-workspace",status="failure"} 1

License: MIT