Refactor configure function, enhance readability in validate functions and improve logging messages

[code-narrator]

The PR was created automatically by CodeNarrator. The following issues were fixed:

1. Refactor the configure function to separate the concerns. This function is doing too many things: setting up logging, loading configuration files, setting up Google credentials, setting up metrics, and initializing Sentry. Each of these tasks should be in its own function. This will make the code easier to read and maintain.
2. In the validate function, instead of checking if a variable is None, use the in keyword to check if the variable exists in the dictionary. This is more Pythonic and easier to read.
3. In the validate_conditional_config function, the code is checking if "vars" and "env" are in supported_choices[chosen_variant] and then iterating over them. This can be simplified by using the get method with a default value of an empty list. This will return an empty list if "vars" or "env" are not in the dictionary, and the for loop will do nothing.
4. The validate_conditional_config function is raising EnvironmentError and ConfigurationError with very similar messages. These could be combined into a single custom exception class that takes the number of missing variables, the missing variable names, and the variant as parameters. This would reduce code duplication and make the code easier to maintain.
5. The logging messages in the configure, validate, and validate_conditional_config functions could be improved. They should include more context about what the function is doing and any important variables. This will make the logs more useful for debugging.

[sonarcloud]

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