docs: remove multi-region example (#1007)

## Description

The multi region example is removed as it doesn't show any new feature
but the deployment into several regions which is AWS standard and known
by the users.

I added a remark to the default example that multi region deployment is
possible. Just to keep it in mind.

.github/workflows/ci.yml

@@ -36,7 +36,6 @@ jobs:
           [
             "runner-default",
             "runner-docker",
-            "runner-multi-region",
             "runner-pre-registered",
             "runner-public",
             "runner-certificates"

examples/README.md

@@ -5,5 +5,4 @@ Please see the readme in per example for more details:
 - [runner-default](runner-default/) The default setup, private subnet, auto register, runner on spot instances.
 - [runner-public](runner-public/) Runner in a public subnet, auto register, runner on spot instances.
 - [runner-docker](runner-docker/) Runners run on the same instance as the agent.
-- [runner-multi-region](runner-multi-region/) Runners in multiple regions.
 - [runner-pre-registered](runner-pre-registered) Runner needs to be preregistered, old setup DEPRECATED.

examples/runner-default/README.md

@@ -13,6 +13,9 @@ This examples shows:
   - Additional security groups that are allowed access to the runner agent
   - Use of `runners.docker.services` to configure docker registry mirror (commented out - uncomment to apply)
 
+Multi region deployment is, of course, possible. Just instantiate the module multiple times with different AWS providers. In case
+you use the cache, make sure to have one cache per region.
+
 ![runners-default](https://github.com/cattle-ops/terraform-aws-gitlab-runner/raw/main/assets/images/runner-default.png)
 
 ## Prerequisite