BUG/ENH: cdf support for multi_file_day xarray, TIMED SABER

[jklenzing]

Description

• Updates the TIMED SABER instrument to use xarray.
• bug fix: merging of xarray datasets now correctly concatenates across epoch. This bug also affects jpl_gps when loading multiple days
• Add drop_dims kwarg to remove unmergable data. (In this case, record0 is a string data stamp)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

import datetime as dt
import pysat

roti = pysat.Instrument('jpl', 'gps', tag='roti')
roti.load(date=dt.datetime(2012, 11, 29), end_date=dt.datetime(2012, 12, 2))

saber = pysat.Instrument('timed', 'saber')
saber.load(date=dt.datetime(2019, 1, 1))

In develop, roti will fail to load multiple days.
SABER should now load a full day of data as an xarray object.

Test Configuration

• Operating system: Monterrey
• Version number: Python 3.10.8

Checklist:

• Make sure you are merging into the develop (not main) branch
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• Add a note to CHANGELOG.md, summarizing the changes
• Update zenodo.json file for new code contributors

[JonathonMSmith]

This looks good to me!