Add concurrency tests for Cinder operations

This patch introduces parallel resource creation and volume attach
scenarios using Python's multiprocessing module. It enables testing
concurrent operations on volumes and snapshots including
attaching multiple volumes to a single server.

Two new configuration options were added:
- `concurrency_tests`: Enables or disables concurrency test execution
- `concurrent_resource_count`: Number of resources to create concurrently

Additionally, a new CI job was added:
cinder-tempest-plugin-lvm-concurrency-tests, which is configured to:
- Run the concurrency tests in serial (tempest_concurrency: 1)
- Avoid hitting environment resource limits by limiting the number
  of simultaneously running tests
- Isolate concurrency logic validation from unrelated Tempest tests

Signed-off-by: Liron Kuchlani <lkuchlan@redhat.com>
Change-Id: Iebbee32966fe91f8a586cdb84e02981101a91968
diff --git a/cinder_tempest_plugin/plugin.py b/cinder_tempest_plugin/plugin.py
index 79c835c..e9583cd 100644
--- a/cinder_tempest_plugin/plugin.py
+++ b/cinder_tempest_plugin/plugin.py
@@ -47,6 +47,9 @@
         config.register_opt_group(conf, config.volume_feature_group,
                                   project_config.cinder_option)
 
+        config.register_opt_group(conf, config.volume_group,
+                                  project_config.concurrency_option)
+
         # Define the 'barbican' service_available option, but only if the
         # barbican_tempest_plugin isn't present. It also defines the option,
         # and we need to avoid a duplicate option registration.
@@ -62,6 +65,7 @@
         """
         opt_lists = [
             (config.volume_feature_group.name, project_config.cinder_option),
+            (config.volume_group.name, project_config.concurrency_option),
         ]
 
         if 'barbican_tempest_plugin' not in sys.modules: