Description of proposed changes

This PR adds the following changes for hyp3 related data loading process/documentation. With the example dataset on Ridgecrest that @cirrusasf provided (https://jzhu-hyp3-dev.s3.us-west-2.amazonaws.com/hyp3-mintpy/Ridgecrest.zip), I have been able to use tropospheric correction and dem error correction as expected, so the hyp3 + mintpy workflow is fully functioning in my opinion (#540), except for the following two aspects:

One small issue is the DEM error correction for the specific Ridgecrest EQ, when we specify a step function on July 4, but the current code could not distinguish if the step func (EQ) happens before or after the SAR acquisition on the same day. This should be an easy fix, will do it in another PR since it's not really related to hyp3. [Update: fixed in #661]

Another is the UTM coordinated related issues: mintpy is by default expecting lat/lon in degrees, thus, a lot of geo-related script/functions might not work well with UTM coordinates. The detailed number of changes is unknown, I created a milestone to keep track of future related changes: https://github.com/insarlab/MintPy/milestone/6.

• prep_hyp3:

  • ensure negative HEADING value (Heading attribute of InSAR products expressed clockwise instead of counter-clockwise for descending scenes ASFHyP3/hyp3-gamma#306)
  • grab CENTER_LINE_UTC from UTCtime directly
  • put P_BASELINE_* to the ifgram specific metadata
  • add STARTING_RANGE from "Slant range near"
  • add RANGE/AZIMUTH_PIXEL_SIZE from hardwired Sentinel-1 info
  • adjust to the new incidence angle file name 'lv_theta'

• stackDict: convert Gamma inc angle to isce/mintpy inc angle convention while loading the data

• docs/dir_structure.hyp3:

  • remove warning for inc angle as the latest HyP3 is producing the correct one now
  • add geometry file path in the template for incidence angle and water mask
  • use Ridgecrest SenT71 dataset for the example in the directory structure

Reminders

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