feat: support export to output path for pull command

[chlins]

This pull request introduces several changes to enhance the functionality of the pull and push operations, as well as refactoring some parts of the codebase. The most significant changes include adding support for specifying an output path for exporting model artifacts, renaming and refactoring the tar.go file, and updating the progress bar style.

Enhancements to pull and push operations:

• cmd/pull.go: Added a new flag --output to specify the output path for exporting the model artifact and updated the runPull function to handle this new configuration. [1] [2]
• pkg/backend/options.go: Introduced a new option WithOutputPath to set the output path for the pull operation. [1] [2]
• pkg/backend/pull.go: Implemented the logic to export the target model artifact to the specified output directory if the outputPath option is set. [1] [2]
• pkg/backend/push.go: Refined the pushIfNotExist function to fetch the manifest from the source storage and push it to the destination, ensuring the content is correctly handled. [1] [2]

Refactoring and codebase improvements:

• pkg/archiver/archiver.go: Renamed from pkg/backend/build/tar.go and refactored the TarFileToStream function to Tar. Added a new Untar function to handle untarring streams to a destination path. [1] [2]
• pkg/backend/build/build.go: Updated the import paths and changed the call from TarFileToStream to archiver.Tar. [1] [2]

Progress bar style update:

• pkg/backend/progress.go: Modified the progress bar style to use a more consistent and simplified style.

[gaius-qi]

Please add option --extract-dir, and add sub-commaned modctl extract.

[gaius-qi]

LGTM