Fallback to LMT on missing source hash

[gapra-msft]

Description

• Feature / Bug Fix: (Brief description of the feature or issue being addressed)
  For sync, when source hash is missing, AzCopy should fall back to LMT comparison instead of skipping the file.
  AzCopy sync --compare-hash should fall back to LMT if MD5 not present on source and destination

• Related Links:

• Issues

• Team thread

• Documents

• [Email Subject]

Type of Change

• Bug fix
• New feature
• Documentation update required
• Code quality improvement
• Other (describe):

How Has This Been Tested?

I have added an e2e test that should cover all scenarios for source hash

1. hash present and equal
2. hash present and not equal
3. hash missing and source LMTafter destination
4. hash missing and source LMT before destination
   Please see the comments in the test for more info

Thank you for your contribution to AzCopy!

[dphulkar-msft]

LGTM. However, one end-to-end test is failing, and the pull request requires a code sync.