Add /account service for the usage of Proposal Discussion Forum pillar

Add new endpoint:

`/account/${stakeKey}`:
```
{
"id": number,
"isRegistered": boolean,
"view": string,
"isScriptBased": boolean
}
```

On the backend side:
1. Add new service (`backend/service/Account.hs`)
2. Create new sql (depend on `stake_address` table)
3. Create new endpoint in API.hs /account/{stakeKey}
4. Create swagger documentation

On the frontend side:
1. Write query logic to `GET /account/${stakeKey}`
2. Pass query to Proposal Discussion Forum: `frontend/src/pages/ProposalDiscussion.tsx`

For the sake of testing results can be compared with [Koios](https://api.koios.rest/#post-/account_info)