Option to concatenate RESORB file (#133)

* s1_orbit.py: add function to concatenate two orbit files to make a larger one

This allows us to extend the time span for RESORB products

* fix the output name and stop time parse. return the outfile

* add tests for RESORB edge case and concatenation function

* rename the pytest for the function

* working version of RESORB concat, with overlap and XML order issue solved

* load OSVs for ANX time crossing without ISCE3 module

* code cleanup

* code cleanup

* notes about concatenation order; option to concatenate RESORB file in the file list; updates on unit test and test data

* remove bad return value from docstring

* fix on padding at tail of the timeframe

* Apply suggestions from code review

Co-authored-by: Scott Staniewicz <scott.stanie@gmail.com>

* reference update to `_covers_timeframe`

* make RESORB concatenation optional

* s1_annotation import style change

* extracting the OSv list merging routine as `merge_osv_list()`; leave a note on OSV list sorting routine

* declaring the orbit time padding as `PADDING_TIME_ORBIT`; option to take the list of orbit files when loading OSV lists

* unit test update

* RESORB combination search attempt into `get_orbit_file_from_list`

* revision on the note regarding the orbit concatenation

* fix on computing relative time wrt. `datetime_orbit_ref`

* RESORB concatenation is optional for `retrieve_orbit_file` and `False` by default

* variable name change; logic fix on checking RESORB pair search result; take care of case when the RESORB pair search failed

* Apply suggestions from code review

Co-authored-by: Gustavo H. X. Shiroma <52007211+gshiroma@users.noreply.github.com>

* docstring revised

* soft-coding the orbit file name slicing index in `_generate_filename`; comment revision on `test_orbit.py`

* Example orbit file name for the reference

* early return

* Apply suggestions from code review

Co-authored-by: Gustavo H. X. Shiroma <52007211+gshiroma@users.noreply.github.com>

* Apply suggestions from code review

Co-authored-by: Heresh Fattahi <hersh.fattahi@gmail.com>

* variable renaming for clarify; sort the input orbit orbit list

* revise comment in `get_resorb_pair_from_list()`

* Ditching out the orbit file order check

* fix on s1_orbit.py

* get rid of the duplicated 30 min of padding in `get_orbit_dict()`

* variable name revision

* description about short search time window; revision about the comments.

* Note about timing design of RESORB

* Apply suggestions from code review

Co-authored-by: Liang Yu <liangjyu@gmail.com>

* import `PADDING_SHORT` from `s1_orbit.py`

* docstring revised

* docstring revision; revision on if statementl docstring for `merge_osv_list()`

* renmove unnecessary comment

* `_get_uct_time_from_osv` to exxtract OSV's UTC time

* adjustment in module import order

* revised docstring for `get_orbit_dict`; get rid of variavles `pad*_time`

* Apply suggestions from code review

Co-authored-by: Scott Staniewicz <scott.stanie@gmail.com>

* leading underscore names for non-public functions

* bump the version

---------

Co-authored-by: Scott Staniewicz <scott.j.staniewicz@jpl.nasa.gov>
Co-authored-by: Seongsu Jeong <seongsu.jeong@jpl.nasa.gov>
Co-authored-by: Scott Staniewicz <scott.stanie@gmail.com>
Co-authored-by: Gustavo H. X. Shiroma <52007211+gshiroma@users.noreply.github.com>
Co-authored-by: Heresh Fattahi <hersh.fattahi@gmail.com>
Co-authored-by: Liang Yu <liangjyu@gmail.com>