Reactive pos-label and pos-description

[jg10-mastodon-social]

Closes #175

• Observable for anyValue, observing subject+predicates
• Observable for description: wrapper around anyValue
• Observable for label: wrapper around anyValue
• Pos-label uses new observable
• Update unit tests using pos-label: list-address-book, pos-list, pos-login, pos-make-findable, pos-resource, pos-rich-link, pos-switch, pos-user-menu
• Pos-description uses new observable
• Pos-value uses observeAnyValue
• Tests have been written
  • all new code is covered by unit tests
  • the happy path of a new feature is covered by an end-to-end test
  • manual explorative tests have been performed
• all dependencies are updated to the latest patch version at minimum
• the CI pipeline passes
• documentation is up-to-date
  • TSDoc style comments on important functions, properties and events
  • stories for new PodOS elements have been added to storybook
  • Readme.md files of PodOS elements have been re-generated
  • N/A architectural decisions are documented as an ADR
  • Changelogs are updated according to Keep a Changelog

[jg10-mastodon-social]

This is a bit different to other observe functions because I've tried to use the stream of changes directly and avoid unnecessary calls to anyValue.

I should perhaps have implemented this through multiple commits to improve clarity, but I did attempt to follow TDD so the tests should correspond to features of this function.

[jg10-mastodon-social]

While observeLabel doesn't call label at all, it does call labelFromUri so I thought this might be a sufficient test without duplicating all of "if nothing is found in the store".

From a TDD perspective, I wrote this as a failing test before implementing

.pipe(map((value) => value ?? labelFromUri(this.uri)));