feat: Google OAuth for login & signup (#6346)

This PR adds Google OAuth for all existing users, allowing users to log in or sign up via their Google account.

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Co-authored-by: Pranav Raj S <pranav@chatwoot.com>
Co-authored-by: Fayaz Ahmed <15716057+fayazara@users.noreply.github.com>
Co-authored-by: Sojan <sojan@pepalo.com>

app/javascript/dashboard/i18n/locale/en/signup.json

@@ -5,6 +5,9 @@
     "TESTIMONIAL_HEADER": "All it takes is one step to move forward",
     "TESTIMONIAL_CONTENT": "You're one step away from engaging your customers, retaining them and finding new ones.",
     "TERMS_ACCEPT": "By creating an account, you agree to our <a href=\"https://www.chatwoot.com/terms\">T & C</a> and <a href=\"https://www.chatwoot.com/privacy-policy\">Privacy policy</a>",
+    "OAUTH": {
+      "GOOGLE_SIGNUP": "Sign up with Google"
+    },
     "COMPANY_NAME": {
       "LABEL": "Company name",
       "PLACEHOLDER": "Enter your company name. eg: Wayne Enterprises",