Fix typos and improve documentation across several files

[Dimitrolito]

This PR addresses several typographical issues across multiple documentation files. The changes include fixing hyphenation errors, correcting article usage, and updating duplicated phrases.

Changes

• Fixed the spelling of "password-protected" in intapi_changelog.md.
• Corrected the use of "an" vs. "a" in server.md and README.md for consistency and clarity.
• Added missing hyphen in "cross-origin" in server.md.
• Removed duplicated phrase "to have" in rules.md.

Checklist

• I have added at least 2 reviewers or the whole pos-v1 team
• I have added sufficient documentation in code
• I will be resolving comments - if any - by pushing each fix in a separate commit and linking the commit hash in the comment reply
• Created a task in Jira and informed the team for implementation in Erigon client (if applicable)
• Includes RPC methods changes, and the Notion documentation has been updated

Testing

• I have manually tested the changes in my local environment.
• I have tested the functionality in the remote devnet.

Additional comments

No additional comments.

[marcello33]

Thanks @Dimitrolito
Can you change the target branch to develop?

[Dimitrolito]

@marcello33
Done! I have changed the target branch to 'develop' as requested