If there are no tags but the form is still shown, the admin
could ask to add an empty tag returning an error 422
unprocessable entity.
Remove if there are no tags available
Create a new table representing tags, composed of a name and color.
They can be used to tag truths and filter them later.
Tags display under the truths they correspond to and can be clicked
to access all truths matching this tag.
Introduce a new element in the top bar to allow navigating to the
tag list, which can be used to create and edit tags for the admin
and used to select a list of tags to filter against for everyone.
Update the database records of the truths to include the tag vector.
As the database query result is a multi-row result, it cannot be
parsed automatically so it needs to be skipped and retrieved
manually.
