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.

---------

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/components/ui/Auth/GoogleOAuthButton.vue

@@ -0,0 +1,96 @@
+<template>
+  <div>
+    <div v-if="showSeparator" class="separator">
+      OR
+    </div>
+    <a :href="getGoogleAuthUrl()">
+      <button
+        class="button expanded button__google_login"
+        :class="{
+          // Explicit checking to ensure no other value is used
+          large: buttonSize === 'large',
+          small: buttonSize === 'small',
+          tiny: buttonSize === 'tiny',
+        }"
+      >
+        <img
+          src="/assets/images/auth/google.svg"
+          alt="Google Logo"
+          class="icon"
+        />
+        <slot>{{ $t('LOGIN.OAUTH.GOOGLE_LOGIN') }}</slot>
+      </button>
+    </a>
+  </div>
+</template>
+
+<script>
+const validButtonSizes = ['small', 'tiny', 'large'];
+
+export default {
+  props: {
+    showSeparator: {
+      type: Boolean,
+      default: true,
+    },
+    buttonSize: {
+      type: String,
+      default: undefined,
+      validator: value =>
+        validButtonSizes.includes(value) || value === undefined,
+    },
+  },
+  methods: {
+    getGoogleAuthUrl() {
+      // Ideally a request to /auth/google_oauth2 should be made
+      // Creating the URL manually because the devise-token-auth with
+      // omniauth has a standing issue on redirecting the post request
+      // https://github.com/lynndylanhurley/devise_token_auth/issues/1466
+      const baseUrl =
+        'https://accounts.google.com/o/oauth2/auth/oauthchooseaccount';
+      const clientId = window.chatwootConfig.googleOAuthClientId;
+      const redirectUri = window.chatwootConfig.googleOAuthCallbackUrl;
+      const responseType = 'code';
+      const scope = 'email profile';
+
+      // Build the query string
+      const queryString = new URLSearchParams({
+        client_id: clientId,
+        redirect_uri: redirectUri,
+        response_type: responseType,
+        scope: scope,
+      }).toString();
+
+      // Construct the full URL
+      return `${baseUrl}?${queryString}`;
+    },
+  },
+};
+</script>
+
+<style lang="scss" scoped>
+.separator {
+  display: flex;
+  align-items: center;
+  margin: var(--space-two) var(--space-zero);
+  gap: var(--space-one);
+  color: var(--s-300);
+  font-size: var(--font-size-small);
+  &::before,
+  &::after {
+    content: '';
+    flex: 1;
+    height: 1px;
+    background: var(--s-100);
+  }
+}
+.button__google_login {
+  background: var(--white);
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  gap: var(--space-one);
+  border: 1px solid var(--s-100);
+  color: var(--b-800);
+}
+</style>