Fix directory permissions for assessment imports

[20wildmanj]

Description

This PR addresses failing unit tests in assessments_controller_spec.rb for importAsmtFromTar by correctly setting directory permissions.

Motivation and Context

Tests were failing due to

1. Archive.in_dir? check being strict, meaning that we skipped over the assessment directory itself
2. When entry is a file, entry.header.mode is passed to mkdir_p, which is in general incorrect. This is because modes might be specified with the file type, e.g. 100644 indicates a file with permissions 0644. See https://unix.stackexchange.com/a/450488 for more details.

This resulted in directories with bad permissions if we process a file and

1. Parent directory was not created yet, either because we skipped over it, or possibly the directory entry comes later, and no other files in the directory were processed yet
2. The file has a type specific mode

To remedy this, the PR

1. defaults to mode 0755 for the creation of parent directories when processing a file
2. chmod when processing directories, to ensure that have the correct permissions if they were created implicitly when processing a file
3. change the in_dir? check to allow for equality

How Has This Been Tested?

Run bundle exec rails spec

See that importing assessments still work manually:

• Unzip and import, see that all files are imported from the tar successfully: hellotar.tar.zip
• Unzip and import, see that all files are imported from the tar successfully:
  homework02-correct.tar.zip

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have run rubocop for style check. If you haven't, run overcommit --install && overcommit --sign to use pre-commit hook for linting
• My change requires a change to the documentation, which is located at Autolab Docs
• I have updated the documentation accordingly, included in this PR

[damianhxy]

LGTM by @20wildmanj