Fix: "Secure microservices with Kong and Ory" docker-compose.yml issues

[tsagkase]

Fixed a couple of issues with kratos-oathkeeper-kong example.

1. Docker image kong:latest breaks kratos-oathkeeper-kong example by having the kong containers exit. Now pinned to kong:2.7.2 which probably was latest when you coded the example seems to work. The relevant container logs:

    $ docker logs kratos-oathkeeper-kong-kong-1 2>&1 | tail -1
    exec /docker-entrypoint.sh: no such file or directory

The same complaint comes up with the platform: linux/arm64 directive and was removed from docker-compose.yml.

2. The hello microservice image did not contain a binary as it failed to build due to missing CGO_ENABLED=0 build directive.

Related Issue or Design Document

The PR concerns a fix to the code linked to by the Secure microservices with Kong and Ory tutorial.

The relevant GitHub issue is #33.

Checklist

• I have read the contributing guidelines and signed the CLA.
• I have referenced an issue containing the design document if my change introduces a new feature.
• I have read the security policy.
• I confirm that this pull request does not address a security vulnerability. If this pull request addresses a security
  vulnerability, I confirm that I got green light (please contact security@ory.sh) from the
  maintainers to push the changes.
• I have added tests that prove my fix is effective or that my feature works.
• I have added necessary documentation within the code base (if appropriate).

Further comments

Docker image pinning is probably a safe practice.

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[gen1us2k]

LGTM