✨ Add better credentials support to new BucketFs API  #75

Summary

Be more explicit and secure on how credentials are used within the bucketfs api.

Replace the default dict in dict credentials mapping passed to the service with a more sophisticated credentials provider,
which e.g. does not accidentally leak authentication information when printing it. Additionally provide more context
that credentials are mapped to specific buckets.

Details

• Add Credential classes/objects
• Credential classes/objects should not leak information when printed
• Credential classes/objects Support explicit request for unsecure output
• Add a more explicit data structure / class for the global credentials mapping/store

Examples / Ideas

Secure & Unsecure Output

credentials = Credentials(username='foo', password='bar')


>>> print(credentials)
Credentials(username: ****, password: ****)

>>> print(f'{credentails:unsecure}')
Credentials(username: foo, password: bar)

Global Credentails Store

store = CredentailStore(
      [
          BucketCredentails(bucket='default', username='user', password='pw'),
          BucketCredentails(bucket='myudfs', username='u', password='secret'),
          ...
     ]
)

store = CredentailStore(
      [
          { 'bucket': 'default', 'username': 'user', 'password': 'pw' },
          { 'bucket': 'myudfs', 'username': 'u', 'password': 'secret' },
          ...
     ]
)

store = credentails.Store(
      [
          credentials.Bucket(name='default', username='user', password='pw'),
          credentails.Bucket(name='myudfs', username='u', password='secret'),
          ...
     ]
)

New Usage

from exasol.bucketfs import Service
from exasol.bucketfs import credentails 

URL = "http://127.0.0.1:1234/"
STORE = credentails.Store(
    credentials.Bucket('default', username='w', password='w')
)
bucketfs = Service(URL, STORE)

Notes

• Printing can/should be implemented by implementing __str__, __format__ and __repr__
• Consider creating a sub module for the credentials code
• Keep support for old credential usage but discourage it
• The Store constructor should support a set of Credentials or just a single one (for simple use cases)
• Think about for which parameters keyword argument passing should be enforced (e.g. username, password?)

Tasks

• Add support for improved credentials
• Add unit and integration tests for this feature(s)
• Update the documentation to use new (more obvious) API for passing the credentials