github(summary): use relative path for artifact link and fix filename

[crazy-max]

fixes #367

Use relative path for artifact link to avoid broken links.

Summary example from integration tests: https://github.com/docker/actions-toolkit/actions/runs/9554693648#summary-26336341867

Artifact link: https://github.com/docker/actions-toolkit/actions/runs/9554693648/artifacts/1610289579

Raw output: https://github.com/docker/actions-toolkit/actions/runs/9554693648/jobs/19145276140/summary_raw

<p>:arrow_down: <a href="./9554693648/artifacts/1610289579"><strong>docker~actions-toolkit~WZAZKH.dockerbuild</strong></a> (5.87 KB)<br>

---

Added extra commit to convert .dockerbuild filename and build name in the summary to unicode entities.

Has been tested on a private repo where a secret value is part of the .dockerbuild filename:

In this case test-docker-action is used as secret value. Here is the raw output of the summary:

<h1>Docker Build summary</h1>
<p>For a detailed look at the build, download the following build record archive and import it into Docker Desktop's Builds view. <br>
Build records include details such as timing, dependencies, results, logs, traces, and other information about a build. <a href="https://docs.docker.com/go/build-summary/">Learn more</a></p><p>:arrow_down: <a href="./9562653800/artifacts/1612120571"><strong>&#x64;&#x6f;&#x63;&#x6b;&#x65;&#x72;&#x7e;&#x74;&#x65;&#x73;&#x74;&#x2d;&#x64;&#x6f;&#x63;&#x6b;&#x65;&#x72;&#x2d;&#x61;&#x63;&#x74;&#x69;&#x6f;&#x6e;&#x7e;&#x31;&#x31;&#x53;&#x55;&#x44;&#x31;&#x2e;&#x64;&#x6f;&#x63;&#x6b;&#x65;&#x72;&#x62;&#x75;&#x69;&#x6c;&#x64;</strong></a> (5.44 KB)<br>
This file includes <strong>1 build record</strong>.</p><p>Find this useful? <a href="https://docs.docker.com/feedback/gha-build-summary">Let us know</a></p><h2>Preview</h2>
<table><tr><th>ID</th><th>Name</th><th>Status</th><th>Cached</th><th>Duration</th></tr><tr><td><code>11SUD1</code></td><td><strong>***/summary.Dockerfile</strong></td><td>:white_check_mark: completed</td><td>0%</td><td>1s</td></tr></table>
<h2>Build inputs</h2>
<pre lang="yaml"><code>context: .
file: summary.Dockerfile
labels:
  - org.opencontainers.image.created=2024-06-18T09:36:08.344Z
  - org.opencontainers.image.description=Test "Docker" Actions
  - org.opencontainers.image.licenses=MIT
  - org.opencontainers.image.revision=63f278762688d23ac87122484821e20de9bc625b
  - org.opencontainers.image.source=https://github.com/docker/***
  - org.opencontainers.image.title=***
  - org.opencontainers.image.url=https://github.com/docker/***
  - org.opencontainers.image.version=master
tags:
  - master
</code></pre>
<hr>

[crazy-max]

This dummy secret is used for testing the behavior of a user having repo name as secret value.