[Improvement] Get credentials from .aws/credentials/[default] when creating config file

[Polina-Prakhova]

Is your feature request related to a problem? Please describe.
When calling the command syndicat init, user must specify an access and a secret keys. This is inconvenient or even unsafe (for example, credentials can be saved in the command history). The ability to get this data from ~/.aws/credentials/[default] should be added to the current implementation.

Describe the expected profit
Fast, easy and more safe way to fill in the configuration file.

Describe the solution you'd like
The command should behave in the same way as now (save the keys if they are explicitly set, otherwise ask the user to enter them). But before displaying a prompt, need to check for their presence in the file. If there is no such file or no credits - display a prompt like before.