Update book content with updated Vale rules

[koozz]

This pull request primarily focuses on improving the readability and consistency of the OSPO book content by addressing grammar, formatting, and terminology issues. Additionally, it includes a minor configuration change in the .vale linting rule. Below is a summary of the most important changes grouped by theme.

Grammar and Style Improvements:

• Updated phrasing for clarity and grammatical correctness, such as replacing "early-stage" with "early stage" and "publicly-visible" with "publicly visible" across multiple sections (ospo-book/content/en/02-chapter.md, ospo-book/content/en/03-chapter.md, ospo-book/content/en/04-chapter.md, ospo-book/content/en/toc.md). [1] [2] [3] [4]
• Improved sentence structure and punctuation, such as fixing "get it" to "get it." for proper punctuation in ospo-book/content/en/02-chapter.md.

Code and Formatting Adjustments:

• Enclosed code identifiers like xz/liblzma in backticks for consistency with markdown formatting in ospo-book/content/en/02-chapter.md. [1] [2]
• Capitalized terms like "Multi-Factor Authentication" and "Continuous Integration" for consistency in ospo-book/content/en/05-chapter.md.

Linting Configuration Change:

• Updated the .vale linting configuration to change the scope from raw to sentence, to improve the accuracy and exclude MarkDown tables of linting checks in .vale/TODO/EmDashes.yml.

Terminology Refinements:

• Replaced "workers/contractors" with "workers and contractors" for better readability in ospo-book/content/en/03-chapter.md.
• Clarified "external/upstream work" to "external and upstream work" for improved understanding in ospo-book/content/en/06-chapter.md.

Fixes: #556

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[alice-sowerby]

Thanks for the updates - the em-dash rule is still creating a few issues, as is the rule about hyphenating adverbs. I can update the writing style guide to tackle the latter.

[koozz]

Thanks for the updates - the em-dash rule is still creating a few issues, as is the rule about hyphenating adverbs. I can update the writing style guide to tackle the latter.

You are totally right, let me check my style locally and/or fix the issue.

[koozz]

Thanks again @alice-sowerby, it should be correct now.

[alice-sowerby]

Looks great! @koozz thank you.