Inject AWS_REGION/AWS_DEFAULT_REGION even if pod doesn't have serviceAccount

**What would you like to be added**:
I would like an option (ideally, in EKS) to inject AWS_REGION and AWS_DEFAULT_REGION into all pods, even if they don't have service accounts. (Right now, this only happens if I have service accounts.)

**Why is this needed**:
I have scenarios where the code running in my pods need to be aware of their AWS region, even if they don't use STS. The main one is if I'm using an application performance monitoring (APM) agent like NewRelic, Splunk, or OpenTelemetry, where I might tag my telemetry with the current region, so I can identify performance issues endemic to one region but not another.

For example, in my newrelic.yml, I do this:
`labels: “region:<%= ENV.fetch(‘AWS_REGION’){ ‘null’ } %>;”`

...and in NewRelic, I can query and filter on application data just from us-east-2 or us-east-1. I need AWS_REGION to be set for this, though.

Read the webhook's existing service-account-based environment injection behavior and determine where AWS_REGION and AWS_DEFAULT_REGION are added. Verify the desired behavior for pods without service accounts while preserving the current behavior for pods that do have them; the payload does not name specific files or tests.

Written by the indexing model from the issue text.