add terse comments to avoid GH issue body limits

[johndarmstrong]

Description

In a large mono repo with multiple libraries, when there is a sizable affected run, typically a release, the output for the comment can exceed the limit for a GitHub Issue Comment Body, resulting in the following error:

PR Detected: Updating the PR Comment with Code Coverage
HttpError: Validation Failed: {"resource":"IssueComment","code":"unprocessable","field":"data","message":"Body is too long (maximum is 65536 characters)"}
    at /home/runner/work/_actions/dkhunt27/action-nx-code-coverage/v1/webpack:/nx-code-coverage/node_modules/@octokit/request/dist-node/index.js:86:1
    at processTicksAndRejections (node:internal/process/task_queues:96:5)

This implements a path forward to expose terse comments that only include the high-level result.app, coverage %, and diffHTML values and drop the Coverage Report <details> block, truncating the output for the comment.

[dkhunt27]

I merged this functionality into v2, but did change the variable name. hide-coverage-reports (true/false) where true is like your concise

fyi, also added hide-unchanged (true/false) where true will hide any coverage output where the diff didn't change