feat: adding reservation flag (#323)

This PR adds a `--reservation` flag. Usually, for teaching, we recommend
relying on SLURM's `magnetic` flag. This way, users will not need to
specify a reservation. However, not all reservations can be made
magnetic nor for all courses. Hence, the introduction of a new flag.

Supersedes PR #285 

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

- **New Features**
- Added support for specifying a SLURM reservation when submitting jobs,
allowing users to include a reservation string during job submission.

- **Documentation**
- Added a section explaining how to use SLURM reservations, including
usage recommendations and best practices for teaching or testing
scenarios.
- Included details about the `--slurm-reservation` flag and noted that
reservation validation and eligibility checks are not performed by the
plugin.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: Filipe G. Vieira <1151762+fgvieira@users.noreply.github.com>

Author: cmeesters

docs/further.md

@@ -618,6 +618,11 @@ This configuration directs SLURM logs to a centralized location, making them eas
 Running Snakemake within an active SLURM job can lead to unpredictable behavior, as the execution environment may not be properly configured for job submission.
 To mitigate potential issues, the SLURM executor plugin detects when it's operating inside a SLURM job and issues a warning, pausing for 5 seconds before proceeding.
 
+### Submittings Jobs into SLURM reservations
+
+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.
+
 ### Frequently Asked Questions
 
 #### Should I run Snakemake on the Login Node of my Cluster?

snakemake_executor_plugin_slurm/__init__.py

@@ -106,6 +106,14 @@ class ExecutorSettings(ExecutorSettingsBase):
             "required": False,
         },
     )
+    reservation: Optional[str] = field(
+        default=None,
+        metadata={
+            "help": "If set, the given reservation will be used for job submission.",
+            "env_var": False,
+            "required": False,
+        },
+    )
 
 
 # Required:
@@ -245,6 +253,9 @@ def run_job(self, job: JobExecutorInterface):
         if self.workflow.executor_settings.requeue:
             call += " --requeue"
 
+        if self.workflow.executor_settings.reservation:
+            call += f" --reservation={self.workflow.executor_settings.reservation}"
+
         call += set_gres_string(job)
 
         if not job.resources.get("runtime"):