Site: redesign shortcodes and partials producing GitHub links

[adutra]

The existing partials and shortcodes generally had bugs:

• Incorrect handling of the -incubating suffix
• Incorrect naming of release tags
• Duplicated logic in many places

This PR introduces new partials:

• A new incubatingSuffix.html partial that correctly outputs the -incubating suffix when appropriate;
• A new polarisGitRef.html partial that outputs a dict with info about a Git ref;
• A new githubPolarisUrl.html partial that outputs standard GitHub URLs for a given ref;
• A new rawGithubPolarisUrl.html partial that outputs raw-style GitHub URLs for a given ref.

It also introduces a new raw-github-polaris.html shortcode that just calls the rawGithubPolarisUrl.html partial.

The existing github-polaris.html shortcode is modified to just call the githubPolarisUrl.html partial.

The old openapiUrl.html partial is removed. It seems to represent an old state of the URL-computing logic found in redoc-polaris.html. It is now superseded by rawGithubPolarisUrl.html.

Finally, the redoc-polaris.html shortcode is modified to call the rawGithubPolarisUrl.html partial.

Checklist

• 🛡️ Don't disclose security issues! (contact security@apache.org)
• 🔗 Clearly explained why the changes are needed, or linked related issues: Fixes #
• 🧪 Added/updated tests with good coverage, or manually tested (and explained how)
• 💡 Added comments for complex logic
• 🧾 Updated CHANGELOG.md (if needed)
• 📚 Updated documentation in site/content/in-dev/unreleased (if needed)

[Copilot]

Pull request overview

Fixes the Hugo github-polaris shortcode so it generates correct GitHub URLs for both unreleased docs (main branch) and released docs (versioned tags), including incubator-era tag suffixes.

Changes:

• Add logic to append -incubating to release tags for versions prior to 1.4.0.
• Fix the release tag prefix to use apache-polaris-... and correctly include the version in the URL.
• Normalize Hugo template whitespace trimming in the generated URL output.

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[adutra]

Note: I'm also deleting openapiUrl.html : it's unused and the template is very similar to github-polaris.html.

Note 2: github-polaris.html is also unused 😆 – but I'm planning to use it soon.

[adutra]

@dimas-b and other reviewers: apologies for the confusion. I broadened the scope of this PR after discovering more places where the wrong incubating suffix logic was being used/duplicated.

In this PR, no logic is duplicated anymore and partials are introduced for both GitHub standard and "raw" URLs.

PTAL again 🙏