prep_hyp3: support burst-wide interferograms from hyp3-isce2

[cirrusasf]

… analysis with mintpy

Description of proposed changes

Reminders

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[yunjunz]

Thank you @cirrusasf for the PR. I am excited to see the burst interferogram going forward. Could you provide an example description of the directory structure, including the actual file names, for the burst interferograms? I assume it's similar to https://mintpy.readthedocs.io/en/latest/dir_structure/#asf_hyp3.

[yunjunz]

Except for my comment above. The rest looks all good to me.

[forrestfwilliams]

Hey @yunjunz thanks for the review. This all looks good to me. I believe @cirrusasf has added the directory structure info you requested and I like using the presence of IW to determine if the product is a burst product. Anything else you'd like to see before merging?

[yunjunz]

Thanks @forrestfwilliams. That's all for this PR. After the service went online, it would be helpful to prepare a small example dataset, similar to RidgecrestSenDT71 and FernandinaSenDT128, for two benefits: 1) users could learn from this dataset to organize their files and directories and grab a idea of what to expect from hyp3+mintpy workflow; 2) if the dataset is small, we could add it to the integration test in mintpy.