feat: [SNOW-2457402] Unify encoding support in SnowCLI

[sfc-gh-kolszewski]

Pre-review checklist

• I've confirmed that instructions included in README.md are still correct after my changes in the codebase.
• I've added or updated automated unit tests to verify correctness of my new code.
• I've added or updated integration tests to verify correctness of my new code.
• I've confirmed that my changes are working by executing CLI's commands manually on MacOS.
• I've confirmed that my changes are working by executing CLI's commands manually on Windows.
• I've confirmed that my changes are up-to-date with the target branch.
• I've described my changes in the release notes.
• I've described my changes in the section below.
• I've described my changes in the documentation.

Changes description

See https://snowflakecomputing.atlassian.net/browse/SNOW-2683933

This change adds new encoding configuration section with following keys:

• file_io - which controls the encoding used on file operations (read, write, open). Uses platform default if not set.
• subprocess - which controls the encoding used on commands run with subprocess. Uses platform default if not set.
• show_warnings - which controls whether a warning should be displayed if SnowCLI discovers encoding mismatch in the environment. True by default.

Encoding settings are read from the configuration by SecurePath's read_text, write_text and open methods. As such, most places in the code where SecurePath was not used for these purposes were refactored to use SecurePath. I did not apply this change where encoding was already explicitly set as 'utf-8'

The change should be transparent to Unix users. Windows users can expect the warning to be displayed.