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.

La issue non indica file, test o punti di ingresso. Inizia mappando il modello di tag esistente e la UI di selezione dei tag, quindi definisci come devono funzionare i tag padre e figlio, i nomi duplicati e più radici. Il lavoro è completato quando la gerarchia può essere amministrata e la selezione di un tag figlio applica i relativi tag padre a una domanda.

Scritto dal modello di indicizzazione a partire dal testo della issue.