Deploy releases to staging-preprod first (#5308)

## Problem

Before releasing new version to production, we'd like to run a set of
required checks on the incoming release.
The simplest approach, which doesn't require many changes — dedicate one
staging region to `preprod` installation.

The proposed changes to the release flow are the following:
- When a release PR is merged into the release branch — trigger
deployment from the release branch to a dedicated staging-preprod region
(for now, it's going to be `eu-west-1` — Ireland)

Corresponding infrastructure PR:
neondatabase/infra#585

## Summary of changes
- Trigger `deploy.dev` workflow with `-f deployPreprodRegion=true` for
release branch

.github/workflows/build_and_test.yml

@@ -1091,8 +1091,9 @@ jobs:
           GH_TOKEN: ${{ secrets.CI_ACCESS_TOKEN }}
         run: |
           if [[ "$GITHUB_REF_NAME" == "main" ]]; then
-            gh workflow --repo neondatabase/aws run deploy-dev.yml --ref main -f branch=main -f dockerTag=${{needs.tag.outputs.build-tag}}
+            gh workflow --repo neondatabase/aws run deploy-dev.yml --ref main -f branch=main -f dockerTag=${{needs.tag.outputs.build-tag}} -f deployPreprodRegion=false
           elif [[ "$GITHUB_REF_NAME" == "release" ]]; then
+            gh workflow --repo neondatabase/aws run deploy-dev.yml --ref main -f branch=main -f dockerTag=${{needs.tag.outputs.build-tag}} -f deployPreprodRegion=true
             gh workflow --repo neondatabase/aws run deploy-prod.yml --ref main -f branch=main -f dockerTag=${{needs.tag.outputs.build-tag}} -f disclamerAcknowledged=true
           else
             echo "GITHUB_REF_NAME (value '$GITHUB_REF_NAME') is not set to either 'main' or 'release'"