"/bin/sh: yum: command not found" while implementing "howto-mutual-tls-file-provided" in the walkthroughs

Issue description: While implementing the walk through available at "howto-mutual-tls-file-provided" at step #3 I came across the below error.

`/bin/sh: yum: command not found`

I was able to work around this issue by using the below Dockerfile instead.

```
FROM public.ecr.aws/appmesh/aws-appmesh-envoy:v1.23.1.0-prod as envoy
FROM public.ecr.aws/amazonlinux/amazonlinux:2

RUN yum update -y && \
yum install -y jq curl unzip less && \
curl "https://awscli.amazonaws.com/awscli-exe-linux-x86_64.zip" -o "awscliv2.zip" && \
unzip awscliv2.zip && \
./aws/install && \
rpm -e --nodeps unzip && \
rm -rf awscliv2.zip ./aws/install && \
yum clean all && \
rm -rf /var/cache/yum

COPY --from=envoy /usr/bin/envoy /usr/bin/envoy
COPY --from=envoy /usr/bin/agent /usr/bin/agent
COPY --from=envoy /aws_appmesh_aggregate_stats.wasm /aws_appmesh_aggregate_stats.wasm

RUN mkdir /keys && chown 1337:1337 /keys

ENV AWS_DEFAULT_REGION=us-west-2
COPY entryPoint.sh /bin/entryPoint.sh
CMD ["/bin/entryPoint.sh"]

```

The Dockerfile has to be updated in the walkthrough to include the line "FROM public.ecr.aws/amazonlinux/amazonlinux:2" so that the yum commands will work.

Open the walkthrough identified as "howto-mutual-tls-file-provided" and inspect the Dockerfile used at step 3. Check the base image before the yum commands, then verify the walkthrough builds successfully with the documented Dockerfile and that the yum error is gone.

Written by the indexing model from the issue text.