[PLAT-815] Smaller set of fixes to get terraform working again

[evan-opal]

Description

Lighter-weight alternative to #19, based on some of the changes I've had staged locally for a while.

Summary of changes is:

• updated versions for EKS cluster + RDS db to modern versions
• updated versions of many of the providers + modules. I didn't go all the way to latest major versions, as that would have taken more work to rewrite the TF here. These are provider + module versions we're using elsewhere, and will work fine for now.
• reworked how we manage name variables here to make it easier to override resource names in a single place, with a single var

Release Notes Description

n/a

Risk

What is the level of risk to the product with this change? And why? (Low, High)

Low

If "High", what monitoring do we have in place to let us know if something goes wrong?

Testing

Tested and this will mostly work off a clean apply - it'll actually fail on creating the helm_release.alb_controller, since the cluster is private and you won't have any network access to it out of the box. Setting up VPN access has always been sorta out-of-scope here, so I'd recommend either:

• pulling the ALB controller out of here and just putting it in the docs
• switching to EKS auto mode like Various updates to modernize the Terraform stack #19 is doing

Checklist

• I followed PR best practices and performed a self-review of my code
• I updated our external documentation (if applicable add links below):