Rails: Convert Rails API to use GET instead of POST

MR: Fix workspaces prerequisites API to GET instead... (!189404 - merged)

Description

We introduced the /internal/kubernetes/modules/remote_development/prerequisites API in Rails: Add API that agent will call to fetch in... (#519261 - closed) . As part of reviewing the agentk code which would utilize this API, the maintainer pointed out that we can make this a GET request.

This issue should address that concern by converting the POST request to a GET request. This is not a breaking change because it was introduced to be utilized by the agentk which has not yet been merged.

Acceptance criteria

• The /internal/kubernetes/modules/remote_development/prerequisites API is a GET request

Implementation plan

• Update ee/lib/ee/api/internal/kubernetes.rb to update the API to a GET request