feat: new flag for SLURM qos (#351)

a new flag `--slurm-qos` has been added to conform with reservations
requiring a particular qos upon job submission.

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Added optional SLURM QoS support for job submissions. Users can
specify a QoS via a new --slurm-qos=<qos> CLI option or corresponding
executor setting; no change occurs when unset.

* **Documentation**
* Added “Using SLURM QoS” under SLURM reservations, explaining how to
configure QoS alongside reservations and the new option.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: cmeesters

docs/further.md

@@ -627,6 +627,10 @@ With `--slurm-efficiency-report` you can generate a table of all efficiency data
 The plugin allows specifying a flag `--slurm-reservation=<name>` to use a particular reservation.
 It does not validate the spelling nor eligibility to this reservation.
 
+### Using SLURM QoS
+
+To use SLURM's quality of service flags (`--qos` to `sbatch`) the plugin allows specifying `--slurm-qos=<qos-string>`, too. Both, the reservation and the qos may be particularly useful in a course setting.
+
 ### Frequently Asked Questions
 
 #### Should I run Snakemake on the Login Node of my Cluster?

snakemake_executor_plugin_slurm/__init__.py

@@ -140,6 +140,14 @@ class ExecutorSettings(ExecutorSettingsBase):
             "This flag has no effect, if not set.",
         },
     )
+    qos: Optional[str] = field(
+        default=None,
+        metadata={
+            "help": "If set, the given QoS will be used for job submission.",
+            "env_var": False,
+            "required": False,
+        },
+    )
     reservation: Optional[str] = field(
         default=None,
         metadata={
@@ -309,6 +317,9 @@ def run_job(self, job: JobExecutorInterface):
         if self.workflow.executor_settings.requeue:
             call += " --requeue"
 
+        if self.workflow.executor_settings.qos:
+            call += f" --qos={self.workflow.executor_settings.qos}"
+
         if self.workflow.executor_settings.reservation:
             call += f" --reservation={self.workflow.executor_settings.reservation}"