Accessibility: Fix aria labels on section buttons

[Menelion]

Why

In current platform.sh docs, there are quite a number of accessibility errors. Most of them are just annoying, but there was one thing that prevented really from using the docs with a screen reader correctly.
Each section has a button to expand it, and this button has an aria-label of "Toggle section". So imagine if each button had the same text: "Toggle section". that's how I see it on the currently released pages.

What's changed

If a button contains an SVG image (correctly hidden with aria-hidden="true" btw), then the aria-label is changed to have the title of the section in question. If however the section title was the text of the button itself (simplified code: <button>{{ .Title }}</button>), then the aria-label was removed as it is not needed anymore: the text between the button tags is read by all screen readers.

Where are changes

Updates are for:

• platform (sites/platform templates)
• upsun (sites/upsun templates)

[flovntp]

Thanks for your contribution