Add i18n comment for Gravatar's signup and login pages

[wellyshen]

Related to 105164-gh-Automattic/gravatar

Proposed Changes

• To add an i18n comment
• To replace the siteName with clientTitle for the purpose of code consistent

Testing Instructions

• Switch to the branch and run it locally (check the doc to setup your dev environment)
• Log out of your WP account
• Go to the log-in page by this URL (you might need to modify your origin), and the footer still works the same.

• Go to the sign-up page by this URL (you might need to modify your origin), and the footer still works the same.

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• Have you written new tests for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the "[Status] String Freeze" label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
• For changes affecting Jetpack: Have we added the "[Status] Needs Privacy Updates" label if this pull request changes what data or activity we track or use (p4TIVU-ajp-p2)?

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-66613

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-66613&env=jetpack

[matticbot]

Here is how your PR affects size of JS and CSS bundles shipped to the user's browser:

App Entrypoints (~60 bytes added 📈 [gzipped])

name           parsed_size           gzip_size
entry-stepper       +147 B  (+0.0%)      +60 B  (+0.0%)
entry-main          +147 B  (+0.0%)      +60 B  (+0.0%)
entry-login         +147 B  (+0.0%)      +60 B  (+0.0%)

Common code that is always downloaded and parsed every time the app is loaded, no matter which route is used.

Legend

What is parsed and gzip size?

Parsed Size: Uncompressed size of the JS and CSS files. This much code needs to be parsed and stored in memory.
Gzip Size: Compressed size of the JS and CSS files. This much data needs to be downloaded over network.

Generated by performance advisor bot at iscalypsofastyet.com.

[a8ci18n]

This Pull Request is now available for translation here: https://translate.wordpress.com/deliverables/7983279

Thank you @wellyshen for including a screenshot in the description! This is really helpful for our translators.

[a8ci18n]

Translation for this Pull Request has now been finished.