Fix typos and improve consistency in slashing-protection documentation

[Pricstas]

• Fixed a redundant word: Removed an extra "format" in "Exports the slashing protection database in the [validator client interchange format] format."

• Grammar improvement: Changed "Predefined networks can provide defaults such the initial state" to "Predefined networks can provide defaults such as the initial state."

• Config cleanup: Standardized wording in docusaurus.config.js by fixing "Github Pages deploying branch" to "GitHub Pages deployment branch."

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Name	Status	Preview	Comments	Updated (UTC)
doc-teku	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	May 14, 2025 3:04am

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[bgravenorst]

Closing in favour of #659