v0.40.0

feat: add `timeouts` to the instance resource + timeouts variable @DaveSpe (#146)

what

• added timeouts variable (object) to the variables.tf file
• added timeouts code block that references the var.timeouts.x variable with default values to the aws_db_instance resource in main.tf
• added variable description in the README.md

why

I ran into an issue where using the module in TF Cloud during creation the run times out.
The instance get's created but due to the run timing out the TF Cloud state does not get updated and each subsequent run would tear down an instance and recreate it, timing out once again.
I added a timeouts variable with default terraform values, which a user can change if they desire in order to accommodate a longer run.