Logout functionality should respect base_url config in api section

[amoghrajesh]

closes: #49534

The logout functionality should respect the "base_url" that is set. It wasn't doing so because there was a hardcoded occurrence: https://github.com/apache/airflow/blob/main/airflow-core/src/airflow/ui/src/layouts/Nav/LogoutModal.tsx#L35.

With base_url set:
Played around a bit on the console:

const baseHref = "/airflow/"
  const baseUrl = new URL(baseHref, globalThis.location.origin);
  const logoutPath = new URL("api/v2/auth/logout", baseUrl).pathname;


logoutPath
'/airflow/api/v2/auth/logout'

Without:

      const baseHref = document.querySelector("head>base")?.getAttribute("href") ?? "";
      const baseUrl = new URL(baseHref, globalThis.location.origin);
      const logoutPath = new URL("api/v2/auth/logout", baseUrl).pathname;
logoutPath
'/api/v2/auth/logout'

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[pierrejeambrun]

Nice thanks.

One small suggestion. But non blocking.