Update the taxonomy manual page
Update the taxonomy manual page

Changes include:

* Fix broken link to taxonomy edit page
* Link to the example guidance on production rather than integration
* Correct the statement about the visibility of taxons. All topic pages exist for all published taxons,
so even ones that aren’t “live” can be found on GOV.UK, if you know where to look.
* Remove out of date text. We don’t really have a concept of a draft taxonomy anymore. The entire
taxonomy is published, and we use “phases” to determine how it’s used on the live site.
* Add a link to the metrics gathering rake task
* Update information about who can tag.
* Update the review date for this page

alphagov/govuk-developer-docs,alphagov/govuk-developer-docs,alphagov/govuk-developer-docs,alphagov/govuk-developer-docs