ci: add workflow for mkdocs (by versions using mike)

[Zvikan]

What does this PR do?

• Add new GH workflow to deploy mkdocs using mike

Motivation

• Project GH pages (https://aws-ia.github.io/terraform-aws-eks-blueprints/) is not updated since we've been using mkdocs manually until now and behind multiple releases.
• Few issues (e.g. Error: context deadline exceeded: when destroying 'eks-cluster-with-new-vpc" #573) caused because of docs are incorrect and need to be fixed and updated docs to be published.
• mike allows us to have multiple versions (per release) of mkdocs, allowing customers to switch docs by release version.

TODO post merge

• Post merge after first release run mike set-default latest --push as landing page will always be latest release version.

More

• Yes, I have tested the PR using my local account setup (Provide any test evidence report under Additional Notes)
• Yes, I have added a new example under examples to support my PR
• Yes, I have created another PR for add-ons under add-ons repo (if applicable)
• Yes, I have updated the docs for this feature
• Yes, I ran pre-commit run -a with this PR

Note: Not all the PRs required examples and docs except a new pattern or add-on added.

For Moderators

• E2E Test successfully complete before merge?

Additional Notes

[vara-bonthu]

👍🏼

[bryantbiggs]

Lets try it, thanks!