fix: Update docs for olderCookieDomain config

[anku255]

Summary of change

This PR updates the docs for olderCookieDomain config option in backend SDKs.

Related issues

• https://github.com/supertokens/supertokens-node/pull/813

Checklist

• [ ] Algolia search needs to be updated? (If there is a new sub docs project, then yes)
• [ ] Sitemap needs to be updated? (If there is a new sub docs project, then yes)
• [ ] Checked for broken links? (Run cd v2 && MODE=production npx docusaurus build)
• [ ] Changes required to the demo apps corresponding to the docs?

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