fix: Add a leading dot while setting the cookie domain

[anku255]

Summary of change

We found that browsers don't add a leading dot if sessionTokenFrontendDomain lacks one, preventing cookies from being shared across subdomains. To ensure consistency, we now add a leading dot to all cookie domain configurations by default.

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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