HDDS-16234. Favicon missing on all non-root pages

[shuan1026]

What changes were proposed in this pull request?

The favicon <link> tags in docusaurus.config.js's headTags used relative href values (e.g. href: 'favicon.ico') with no leading /. Since there's no <base> tag on the page, browsers resolve these relative to the current page URL rather than the site root. This only happened to work on / (resolves to /favicon.ico, 200); on any other page it resolved to a nested, non-existent path (e.g. /blog/favicon.ico, 404), so the favicon failed to load on every non-root page (docs, blog, roadmap, etc.).

This PR makes the three headTags favicon entries build their href from the site's baseUrl instead of hardcoding a bare relative path, so they always resolve to the site root regardless of page depth.

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-16234

How was this patch tested?

Reproduced the bug first, then verified the fix, using docker compose

• Before the fix, curl against /, /docs/.../ozone-manager/, and /blog/ all emitted the same relative href="favicon.ico" markup, but the resolved nested path (e.g. /docs/.../ozone-manager/favicon.ico) returned 404 while the root path returned 200 — confirming the bug.
• After the fix, the same three pages emit href="/favicon.ico" (and favicon.svg, apple-touch-icon.png), which all resolve to 200 regardless of page depth.

Before the fix:

After the fix:

[jojochuang]

@shuan1026 thanks for the report. Please consider including a screenshot in the future.