[Feature] - Create backup of an Astra Database

Before allowing to clone databases from the user interface it could be valuable for users to clone DB with backup/restore mechanism

- Backup an Astra Database

```
astra db backup mydb \
  -k,--keyspace ks1
  --tables t1,2
  -d,--dest ./tmp
```

- Backup an Astra Database Schema

```
astra db export-schema mydb \
  -k,--keyspace ks1
  --tables t1,2
  -d,--dest ./tmp
```


  