feat(magstats-step): calculate deltajd

[dirodriguezm]

---

Summary of the changes

Adds method to calculate deltajd.

Updates mongo object model with deltajd field

Closes #306

About this PR:

• You added the necessary documentation for the team to understand your work.
• You linked this PR to the corresponding issue or user story.
• Your changes fulfill the Definition of Done of the issue or user story.
• Your changes were tested with manual testing before being submitted.
• Your changes were tested with automatic unit tests.
• Your changes were tested with automatic integration tests.

[codecov]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (b0e0774) 60.89% compared to head (0c4e3ff) 66.59%.
Report is 40 commits behind head on main.

❗ Current head 0c4e3ff differs from pull request most recent head 6b794db. Consider uploading reports for the commit 6b794db to get more accurate results

Files	Patch %	Lines
lightcurve-step/lightcurve_step/step.py	0.00%	4 Missing ⚠️
libs/db-plugins/db_plugins/db/mongo/models.py	0.00%	1 Missing ⚠️
magstats_step/magstats_step/core/magstats.py	94.44%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #307      +/-   ##
==========================================
+ Coverage   60.89%   66.59%   +5.70%     
==========================================
  Files           3       23      +20     
  Lines         179     1443    +1264     
==========================================
+ Hits          109      961     +852     
- Misses         70      482     +412     

Flag	Coverage Δ
unittest	66.59% <88.67%> (+5.70%)	⬆️

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