docs: Update docs site header to match dagger.io

[vikram-dagger]

No description provided.

[vikram-dagger]

Notes:

• The font and style is different. This will need a change to the docs site theme/CSS. Maybe @crjm can help with this?
• Should Get involved -> Get Involved, on both sites?
• I can't find a way to move the search bar down, I believe this will need some customization to the theme/CSS so needs @crjm or someone else familiar with front-end UX

[github-actions]

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