add preprocessing step

[oberonia78]

This PR adds the preprocessing step into the DSWx-SAR workflow. The preprocessing includes

• reading ancillary data such as dem, hand, worldcover, and reference water and relocating them into the mosaic rtc grid.
• applying filter to the rtc images.

[oberonia78]

@seongsujeong Thank you for your comments. It seems it requires more clearing up. I just finished fixing the code based on your comments. For your information, dummpy_dswx_s1.py will be replaced with the new files. So, I did not modify the code for this.

[seongsujeong]

@oberonia78 Thanks for the information. I'll disregard dummpy_dswx_s1.py when reviewing the PR.

[oberonia78]

@seongsujeong I revised the PR based on the comments. Let me know if you have any comments. If not, let's merge it ASAP.

[oberonia78]

@seongsujeong All bugs were corrected and docstrings were added. Let me know if you have more comments.

[seongsujeong]

@oberonia78 one more comment here Please make sure to check that out before merging this PR.