Renamed gradual→split deployments (14 files)

[sudip94373748-dotcom]

Summary

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Documentation checklist

• Is there a changelog entry ([guidelines]whttps://developers.cloudflare.com/style-guide/documentation-content-strategy/content-types/changelog/))? If you don't add o — how will our customers find out? Changelogs are automatically posted to RSS feeds, the Discord, and X.
• The change adheres to the documentation style guide.
• If a larger change - such as adding a new page- an issue has been opened in relation to any incorrect or out of date information that this PR fixes.
• Files which have changed name or location have been allocated redirects.

[github-actions]

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