SNOW-2865734: Fix unnecessary token caching and username_password_mfa auth

[sfc-gh-pbulawa]

This pull request fixes the missing authenticator type for username/password with MFA token caching (SF_AUTHENTICATOR_USR_PWD_MFA) and adds comprehensive tests to verify its behavior. It ensures that MFA tokens are only cached for this authenticator and not for the default username/password authentication. The changes include updates to the core logic, constants, and test suites.

Authenticator logic and constants:

• Added the SF_AUTHENTICATOR_USR_PWD_MFA constant in snowflake/client.h and updated Authenticator.cpp to recognize it, mapping it to the AUTH_USR_PWD_MFA type.
• Updated authentication and secure storage logic to handle AUTH_USR_PWD_MFA separately, ensuring MFA token caching only applies to this type and not to the default authenticator.

Testing enhancements:

• Added two new test suites: test_usr_pwd_mfa (for MFA token caching) and test_default_auth (for default auth without MFA token caching), with corresponding CMake configurations and Wiremock login responses.
• Implemented tests in test_usr_pwd_mfa.cpp to verify successful connection and correct MFA token caching behavior for the new authenticator.
• Implemented tests in test_default_auth.cpp to ensure that MFA tokens are not cached for default username/password authentication.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.84%. Comparing base (b282949) to head (80a72da).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #997      +/-   ##
==========================================
+ Coverage   80.74%   80.84%   +0.10%     
==========================================
  Files         137      137              
  Lines       12077    12078       +1     
==========================================
+ Hits         9751     9764      +13     
+ Misses       2326     2314      -12     

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