Update API docs footer (flutter#150347)

Update API docs footer with a cookie banner (go/cookiebanner) using the
glue banner (go/glue-cookiebar)

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel
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<!-- Links -->
[Contributor Guide]:
https://github.com/flutter/flutter/wiki/Tree-hygiene#overview
[Tree Hygiene]: https://github.com/flutter/flutter/wiki/Tree-hygiene
[test-exempt]:
https://github.com/flutter/flutter/wiki/Tree-hygiene#tests
[Flutter Style Guide]:
https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo
[Features we expect every widget to implement]:
https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo#features-we-expect-every-widget-to-implement
[CLA]: https://cla.developers.google.com/
[flutter/tests]: https://github.com/flutter/tests
[breaking change policy]:
https://github.com/flutter/flutter/wiki/Tree-hygiene#handling-breaking-changes
[Discord]: https://github.com/flutter/flutter/wiki/Chat
[Data Driven Fixes]:
https://github.com/flutter/flutter/wiki/Data-driven-Fixes

Author: mit-mit

dev/docs/analytics-footer.html

@@ -2,3 +2,8 @@
 <noscript><iframe src="https://www.googletagmanager.com/ns.html?id=GTM-ND4LWWZ"
 height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript>
 <!-- End Google Tag Manager (noscript) -->
+<!-- Cookie Banner -->
+<div class="glue-footer"></div>
+<button aria-hidden="true" class="glue-footer__link glue-cookie-notification-bar-control">Cookies management controls</button>
+<script src="https://www.gstatic.com/glue/cookienotificationbar/cookienotificationbar.min.js" data-glue-cookie-notification-bar-category="2B"></script>
+<!-- End Cookie Banner -->

dev/docs/analytics-header.html

@@ -5,3 +5,6 @@
 'https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f)
 })(window,document,'script','dataLayer','GTM-ND4LWWZ');</script>
 <!-- End Google Tag Manager -->
+<!-- Cookie Banner -->
+<link rel="stylesheet" href="https://www.gstatic.com/glue/cookienotificationbar/cookienotificationbar.min.css">
+<!-- End Cookie Banner -->