Snowflake: Support passing OAuth scope parameter in client_credentials flow

[Vishalup29]

Description

This PR adds support for passing an optional OAuth scope parameter when using the
client_credentials grant type in SnowflakeHook.get_oauth_token.

Many identity providers (Okta, Auth0, Azure AD, corporate IdPs) require or recommend including a scope
in client-credential OAuth exchanges. Currently, Airflow cannot send a scope value, forcing users to
apply custom patches or weaken their IdP requirements.

This PR introduces an optional extra field on the Snowflake connection:

extra: {"oauth_scope": "your-scope-value"}

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When present and the grant_type is client_credentials, the hook will send:

scope=

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in the POST body to the token endpoint.
If no scope is provided, the existing behavior is unchanged.

Tests

This PR updates the OAuth unit tests to validate:

• Scope is not included for refresh token grant (existing behavior unchanged)
• Scope is included when:
  • grant_type=client_credentials
  • oauth_scope is provided
• Scope is omitted when the field is empty or not provided
• Existing OAuth tests continue to pass untouched

Cross-provider compatibility

This matches patterns already used in Azure OAuth (azure_oauth_scope).

Related Issue

Closes #58815

[boring-cyborg]

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[potiuk]

Already merged in #58815