"All today's stories" links

The 'topics' bar at the bottom of fronts pages is made up of two parts.

- The 5 most popular (non-section) keyword tags in the stories contained on that front (this is implemented in #7101)
- Sometimes there is also an `All today's stories` link at the beginning of the list (highlighted below).

## Status quo for "All today's stories"

Generally speaking, for a tag or section page the `allPath` link should link to the non-editionalised front which displays all stories in that tag or section, e.g. `All today's stories` on the `uk/lifeandstyle` front will link to `lifeandstyle/all`.

The `allPage` URL is not defined in the CAPI or facia-press models, so Frontend [uses a heuristic](https://github.com/guardian/frontend/blob/f64c5b681f53a9c87ae1e76c529d08b3ad16ef6b/common/app/model/PressedPage.scala#L131-L155) to find the relevant path.

### Current heuristic for generating an 'allPath'

Roughly: if the page id matches the section id of at least one tag belonging to a curated story in that page, then remove the edition (if any) from the page id and add '/all' to the end of it.

> e.g.
> `uk/lifeandstyle` -> `lifeandstyle/all`

This won't always yield a path. If it doesn't, then Frontend tries to find a path ending in '/all' in one of the _treats_ on the front. (This is how the `allPath` for the `/uk` front gets determined.)

## Issues/Questions

- Is the `allPath` functionality in Frontend currently working as intended? (the `/uk` front's `All today's stories` link goes to `tone/letters/all` -- drawn from a treat on the front -- which is unlikely to be what users would expect).
- More generally, what is the intended functionality for this link?
- Worth noting that there don't appear to be tests for this functionality, and we haven't been able to find documentation of the original intention yet.
- Navigation/discovery is a good aim, but from preliminary exploration it looks like these links get very little traffic (e.g. ~20 clicks per day on the UK front).
- SEO has been mentioned a few times; do we know how to clarify its role in SEO?
- UX may be looking into this in the near future, although no specific work is planned.
- Do we need to migrate this over to DCR as part of the 1% test? If we're unsure, how can we find out the information needed to make a decision?