First version of a new benchmark to test larger OLTP workload (#11053)

## Problem

We want to support larger tenants (regarding logical database size,
number of transactions per second etc.) and should increase our test
coverage of OLTP transactions at larger scale.

## Summary of changes

Start a new benchmark that over time will add more OLTP tests at larger
scale.
This PR covers the first version and will be extended in further PRs.

Also fix some infrastructure:
- default for new connections and large tenants is to use connection
pooler pgbouncer, however our fixture always added
`statement_timeout=120` which is not compatible with pooler
[see](https://neon.tech/docs/connect/connection-errors#unsupported-startup-parameter)
- action to create branch timed out after 10 seconds and 10 retries but
for large tenants it can take longer so use increasing back-off for
retries

## Test run

https://github.com/neondatabase/neon/actions/runs/13593446706

.github/actions/neon-branch-create/action.yml

@@ -84,7 +84,13 @@ runs:
           --header "Authorization: Bearer ${API_KEY}"
           )
 
-        role_name=$(echo $roles | jq --raw-output '.roles[] | select(.protected == false) | .name')
+        role_name=$(echo "$roles" | jq --raw-output '
+          (.roles | map(select(.protected == false))) as $roles |
+          if any($roles[]; .name == "neondb_owner")
+          then "neondb_owner"
+          else $roles[0].name
+          end
+        ')
         echo "role_name=${role_name}" >> $GITHUB_OUTPUT
       env:
         API_HOST: ${{ inputs.api_host }}
@@ -107,13 +113,13 @@ runs:
             )
 
           if [ -z "${reset_password}" ]; then
-            sleep 1
+            sleep $i
             continue
           fi
 
           password=$(echo $reset_password | jq --raw-output '.role.password')
           if [ "${password}" == "null" ]; then
-            sleep 1
+            sleep $i # increasing backoff
             continue
           fi