Convert this action to a NodeJS action to improve security

[christian-kreuzberger-dtx]

Right now this action provides an attack vector that could leak API Credentials to the Dynatrace API.
Unfortunately, this is by design of GH Actions when you use composite actions with Bash Scripts.

The only way to work around this would be to rewrite parts of this action in NodeJS, and access the secrets from input rather than from an environment variable, same as we do in gh-action-send-event:
https://github.com/keptn/gh-action-send-event/blob/main/index.js#L5-L7

We can still download can execute install.sh from the dynatrace-operator. We just need to make sure (e.g., by calling env within that script) that no environment variables with the Token or the API URl are available.

Definition of Done

• Security relevant environment variables can no longer be accessed by bash scripts via env
• Main part of the action is rewritten into a NodeJS action, same as https://github.com/keptn/gh-action-send-event