Create a subcommand `cosmian configure`

The idea is to facilitate the generation of the configuration file.

One could run: 
```
cosmian configure
```
and `cosmian` will prompt multiple questions where user will have to give:
- KMS server URL
- Findex server URL
- Authentication parameters for KMS (cert, JWT or nothing)
- Authentication parameters for Findex server (cert, JWT or nothing)
- GMAIL parameters for KMS
- 