feat: Support standard environment variables

[PSanetra]

Closes #81

Changes

• Make previously required parameters of oauth_channel.create_oauth2_client_credentials_channel() and oauth_channel.create_camunda_cloud_channel() optional

API Updates

New Features (required)

oauth_channel.create_oauth2_client_credentials_channel() and oauth_channel.create_camunda_cloud_channel() support the following environment variables:

• ZEEBE_ADDRESS
• CAMUNDA_CLUSTER_ID
• CAMUNDA_CLUSTER_REGION
• CAMUNDA_CLIENT_ID
• ZEEBE_CLIENT_ID
• CAMUNDA_CLIENT_SECRET
• ZEEBE_CLIENT_SECRET
• CAMUNDA_OAUTH_URL
• ZEEBE_AUTHORIZATION_SERVER_URL
• CAMUNDA_CREDENTIALS_SCOPES
• CAMUNDA_TOKEN_AUDIENCE
• ZEEBE_TOKEN_AUDIENCE

Checklist

• Unit tests
• Documentation

[CLAassistant]

All committers have signed the CLA.

[coveralls]

Pull Request Test Coverage Report for Build 11257124077

Details

• 45 of 47 (95.74%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.07%) to 96.813%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pyzeebe/channel/oauth_channel.py	9	11	81.82%

Totals
Change from base Build 11248787810:	-0.07%
Covered Lines:	1124
Relevant Lines:	1161

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💛 - Coveralls

[felicijus]

@dimastbk I would like to check the Camunda Cloud implementation side of this again, review should be in tomorrow.

@PSanetra thank you, you were quicker I also had this planned as a prull-request.