Is your feature request related to a problem? Please describe.
I currently have tags that are more or less hierarchical in nature. an example would be exactly the one given on the website where you have projects (proj) and types of work (type).
I would now like to display a Dashboard (pie chart to be precise) showing the the distribution of type of work for one project.
If this is possible, I have not found out how I can do this.
(And from looking at the code for 2-3min I don't think it is possible as Dashboard Entries only save the tags keys but no values)

Describe the solution you'd like
I would like to be able to enter something like "proj:traggo type" in the Tags field of a Database Entry to show me a graph of tag "type" filtered for entries that also have the key-value pair "proj:traggo".

Describe alternatives you've considered
An additional field in the Database Entry that defines filters would also be a viable option, otherwise I do not see how I could do this without basically duplicating my type tags for all projects (so I would have "type-traggo:" and "type-gotify:" instead of just "type:".
This is a viable solution if you do not have many projects but the amount of work required to do this increases linearly with the amount of projects while also getting harder and harder to manage.

Additional context
As mentioned above, this change is mostly useful for people with a lot of projects. For example students (like me) that have a lot of courses and personal projects and would like to create graphs for each course in order to check the time-breakdown for each.
I am pretty sure this change would also allow for some other things that I cannot think of.

A more elaborate system would be based on my suggestion but extended by a 'not equal' option. So you could write something like "!proj:traggo type" to display a graph of types where the entries do not contain the "proj:traggo" key-value pair. This addition would allow for things like easy archiving, you could add "archive:true" to things that should be archived and then add "!archive:true" to all graphs so they do NOT display these entries anymore.