feat: support extra head tags

[antonio-ivanovski]

Summary

This PR adds support for extra head tags per page via Frontmatter config.

Related Issue

#1121

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

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[Timeless0911]

Thxs, can you add a seperate new fixture for this feature instead?

[antonio-ivanovski]

Thxs, can you add a seperate new fixture for this feature instead?

Done in 598cdc9

[antonio-ivanovski]

Made changes as discussed in #1121

• Now the header attributes are being applied in the build step
• Made some changes to the loadFrontMatter typing so get better typing support on the build side.

@Timeless0911 please re-review

[antonio-ivanovski]

@Timeless0911 please also consider the extension to this PR #1168

[Timeless0911]

This PR looks like it can be closed now since #1168

[antonio-ivanovski]

This PR looks like it can be closed now since #1168

Sounds good, only created it as separate PR to allow the one being approved and merged without the other in case it doesn't fit into the vision for Rspress.

Feel free to close this PR if not needed.