support auto_path for `isce2/alosStack`

[yunjunz]

Description of proposed changes

• defaults.auto_path.py:

  • add AUTO_PATH_ISCE_ALOS global var
  • add get_reference_date() to grab ref_date from the alosStack.xml file
  • update get_auto_path() for isce2/alosStack

• Rename the following offensive var abbreviations

  • m_shelve --> ref_shelve
  • m_date12 --> ref_date12
  • m_ifg_file --> ref_ifg_file

Reminders

• [x] Pass Pre-commit check (green)
• [x] Pass Codacy code review (green)
• [x] Pass Circle CI test (green)
• [x] Make sure that your code follows our style. Use the other functions/files as a basis.
• [x] If modifying functionality, describe changes to function behavior and arguments in a comment below the function declaration.