Replace ad-hoc Bash reliant on local executables with TF resources

[rehevkor5]

The TF stack currently relies on local execution of https://github.com/ExpediaGroup/apiary-data-lake/blob/master/scripts/mysql-user.sh which relies on local availability of aws, mysql, and jq executables.

This could be replaced by use of https://www.terraform.io/docs/providers/aws/d/secretsmanager_secret_version.html for AWS secret retrieval, and https://www.terraform.io/docs/providers/mysql/index.html for interacting with MySQL.

[massdosage]

How much of an issue is this? Could we get a PR? I'm just trying to clean up issues which have been open for months with no movement on them.

[mroark1m]

It is definitely a stumbling block to using the module... maybe we can at least doc it in the README for now?

[mroark1m]

Here's a PR that updates the README (Ignore the "Issue 17" bit, I grabbed the wrong issue number): #139