Add broken link checker to deploy preview workflow

[robbymilo]

for https://github.com/grafana/website/issues/29598

This PR adds a broken link job to the deploy preview workflow. It refactors the website build step to upload an artifact which is then used simultaneously to deploy the preview and check links.

Unlike our link checker in the website repo, this replaces muffet with standard Golang HTTP requests. The link check process is:

1. Download the built website artifact.
2. A Go script walks the dist dir to build a list of pages.
3. Nginx is configured, tested, and spun up.
4. Each page of the build is crawled and every link is checked if it hasn't already been checked.
5. A comment is added to the PR describing the broken links and where they occur (see screenshot). The comment is updated on subsequent runs.

Todo:

• revert broken link test changes
• support redirects defined in website repo
• support redirects generated from mounted content, ex ../image-rendering/.
• support mounted content

[github-actions]

Readability report

File	AutomatedReadability	ColemanLiau	FleschKincaid	FleschReadingEase	GunningFog	LIX	SMOG
docs/sources/review/test-documentation-changes-test/index.md	$${7.01\space\color{black}(Δ+0.00)}$$	$${10.27\space\color{black}(Δ+0.00)}$$	$${8.61\space\color{black}(Δ+0.00)}$$	$${52.35\space\color{black}(Δ+0.00)}$$	$${10.56\space\color{black}(Δ+0.00)}$$	$${40.89\space\color{black}(Δ+0.00)}$$	$${11.21\space\color{black}(Δ+0.00)}$$
docs/sources/whats-new.md	$${9.69\space\color{black}(Δ+0.00)}$$	$${13.09\space\color{black}(Δ+0.00)}$$	$${9.74\space\color{black}(Δ+0.00)}$$	$${46.61\space\color{black}(Δ+0.00)}$$	$${11.47\space\color{black}(Δ+0.00)}$$	$${70.33\space\color{black}(Δ+0.00)}$$	$${11.21\space\color{black}(Δ+0.00)}$$

View metric targets

Metric	Range	Ideal score
AutomatedReadability	6 (very easy read) to 14 (extremely difficult read)	8 or less
ColemanLiau	6 (very easy read) to 17 (extremely difficult read)	9 or less
FleschKincaid	6 (very easy read) to 17 (extremely difficult read)	8 or less
FleschReadingEase	100 (very easy read) to 0 (extremely difficult read)	70 or more
GunningFog	6 (very easy read) to 17 (extremely difficult read)	10 or less
LIX	20 (very easy read) to 60+ (extremely difficult read)	35 or less
SMOG	6 (very easy read) to 17 (extremely difficult read)	10 or less

[github-actions]

💻 Deploy preview available (update deploy preview workflow with broken link check):

• https://deploy-preview-writers-toolkit-1331-zb444pucvq-vp.a.run.app/docs/writers-toolkit/

[github-actions]

🔗 Broken links report (Add broken link checker to deploy preview workflow): 2 broken links total.

Broken links in files changed in this PR:

File	Broken link
docs/sources/whats-new.md:26:55	/docs/test/writers-toolkit/write/shortcodes/

All other broken links:

File	Broken link
docs/sources/review/cla-assistant/index.md:13:205	/docs/grafana/latest/developers/cla/

Download the full links report artifact.

[github-actions]

💻 Deploy preview available (Add broken link checker to deploy preview workflow):

• https://deploy-preview-writers-toolkit-1331-zb444pucvq-vp.a.run.app/docs/writers-toolkit/