feat: add rule-specific container configuration option (#30)

docs/further.md

@@ -28,6 +28,24 @@ SNAKEMAKE_AWS_BATCH_REGION
 SNAKEMAKE_AWS_BATCH_JOB_QUEUE
 SNAKEMAKE_AWS_BATCH_JOB_ROLE
 
+# Rule-Specific Container Images
+
+By default, all jobs use the global container image specified via `--container-image`. However, you can specify a different container image for individual rules using the `aws_batch_container_image` resource parameter:
+
+```python
+rule my_rule:
+    input:
+        "input.txt"
+    output:
+        "output.txt"
+    resources:
+        aws_batch_container_image="my-custom-image:tag"
+    shell:
+        "process_data.sh {input} {output}"
+```
+
+This allows you to use different containers with specialized tools for different rules within the same workflow, rather than requiring all tools to be present in a single container.
+
 # Example
 
 ## Create environment

snakemake_executor_plugin_aws_batch/__init__.py

@@ -132,11 +132,17 @@ def run_job(self, job: JobExecutorInterface):
         # argument 'external_job_id'.
 
         try:
+            # Use rule-level container image if specified via resources,
+            # otherwise fall back to global container image
+            container_image = job.resources.get(
+                "aws_batch_container_image", self.container_image
+            )
+
             job_definition = BatchJobBuilder(
                 logger=self.logger,
                 job=job,
                 envvars=self.envvars(),
-                container_image=self.container_image,
+                container_image=container_image,
                 settings=self.settings,
                 job_command=self.format_job_exec(job),
                 batch_client=self.batch_client,