TAG hierarchy Support

## Is your feature request related to a problem? Please describe

It is possible that questions can be considered different based on tags attached. Adding tags shouldn't become burden while asking questions.

## Describe the solution you'd like

Supporting Tag Hierarchy support.

- it's a group of groups, nothing but Acyclic graphs (i.e. Trees).
- Nodes can also have the same name. for example: Maintenace can be part of system group / infra group etc. in this case using UI dropdown user can select relevant groups based on his question.
- can Also have multiple roots (i.e. graphs / trees) if admin doesn't choose to join them to a single parent.

an Example hierarchy
```
HR
├── location (name)
│ └── sub-location (name)
├── Pay Slip
└── Admin

Infra
├── location (name)
│ └── sub-location (name)
├── admin
└── maintenance
└── prod support
```

If they chose to tag child tag (all the parents would also apply to that question).

It is also helpful for those who take ownership for answering these questions. Tag Hierarchy will enhance question visibility especially when people track questions based on tags

## Describe alternatives you've considered

A clear and concise description of any alternative solutions or features you've considered.

Das Issue nennt keine Dateien, Tests oder Einstiegspunkte. Beginne damit, das bestehende Tag-Modell und die UI zur Tag-Auswahl zu erfassen, und definiere anschließend, wie übergeordnete und untergeordnete Tags, doppelte Namen und mehrere Wurzeln funktionieren sollen. Als abgeschlossen gilt die Arbeit, wenn die Hierarchie verwaltet werden kann und die Auswahl eines untergeordneten Tags dessen übergeordnete Tags auf eine Frage anwendet.

Vom Indexierungsmodell aus dem Issue-Text verfasst.