When the WOTD block is displayed, export the feed as a page alternate

Problem/Motivation

When the WOTD block is present on a page, the WOTD feed may be considered as one of the alternate representations of the page, so add a meta alternate for it.

Steps to reproduce

Place the WOTD block on a page. Observe how the meta alternate is not added yet.

Proposed resolution

Add it. See web/core/modules/views/src/Plugin/views/style/Rss.php#attachTo for an example of how to do it; and the HEAD version on /rss.xml for how it must look in the HTML source.

Remaining tasks

Do it.

User interface changes

On RSS-enabled browsers and application (e.g. the "RIP Opera" RSS aggregator, the RSS feed will be exposed.

API changes

None.
no

Data model changes