Accessibility Updates (#16633)

* Fixed accessibility issues in home page

Signed-off-by: ChaitanyaKaranam <karanam.krishna.25@gmail.com>

* Fixed accessibility issues for docs/home page

Signed-off-by: chaitanyakaranam <chaitanya.karanam@yahoo.com>

* Fixed accessibility issues for /partners page

Signed-off-by: chaitanyakaranam <chaitanya.karanam@yahoo.com>

* Fixed accessibility issues for /community page

Signed-off-by: chaitanyakaranam <chaitanya.karanam@yahoo.com>

* Update layouts/partials/header.html

Co-Authored-By: Tim Bannister <tim@scalefactory.com>

* Update layouts/partials/footer-scripts.html

Co-Authored-By: Tim Bannister <tim@scalefactory.com>

* Update layouts/index.html

Co-Authored-By: Tim Bannister <tim@scalefactory.com>

* Update content/en/partners/_index.html

Co-Authored-By: Tim Bannister <tim@scalefactory.com>

* Update content/en/community/_index.html

Co-Authored-By: Tim Bannister <tim@scalefactory.com>

* Added missing quotes

* Added landmark roles for search bar and footer

Signed-off-by: chaitanyakaranam <chaitanya.karanam@yahoo.com>

* Changed images alt text

Changed alt text from 'kubernetes community' to 'Kubernetes Conference Gallery'

* Removed verb from iframe title

Signed-off-by: chaitanyakaranam <chaitanya.karanam@yahoo.com>

* Change alt text for GitHub image

Co-Authored-By: Tim Bannister <tim@scalefactory.com>

* Few alt text changes

* Modified alt text

layouts/partials/footer-scripts.html

@@ -1,4 +1,4 @@
-<button class="flyout-button" onclick="kub.toggleToc()"></button>
+<button class="flyout-button" onclick="kub.toggleToc()" aria-label="Toggle table of contents visibility"></button>
 
 <script>
 // hide docs nav area if no nav is present, or if nav only contains a link to the current page