Add option to add Observed Spectrum (2)

[atharva-2001]

Recreation of PR #1761

Description

PR #1761 was reverted, this is a duplicate of that PR, having the exact same commits.

Motivation and context

How has this been tested?

• Testing pipeline.
• Other.

Examples

Type of change

• Bug fix.
• New feature.
• Breaking change.
• None of the above.

Checklist

• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
  • (optional) I have built the documentation on my fork following the instructions.
• I have assigned and requested two reviewers for this pull request.

[review-notebook-app]

Check out this pull request on 

See visual diffs & provide feedback on Jupyter Notebooks.

---

Powered by ReviewNB

[tardis-bot]

Before a pull request is accepted, it must meet the following criteria:

• Is the necessary information provided?
• Is this a duplicate PR?
  • If a new PR is clearly a duplicate, ask how this PR is different from the original PR?
  • If this PR is about to be merged, close the original PR with a link to this new PR that solved the issue.
• Does it pass existing tests and are new tests provided if required?
  • The test coverage should not decrease, and for new features should be close to 100%.
• Is the code tidy?
  • No unnecessary print lines or code comments.

[codecov]

Codecov Report

Merging #1810 (786ac89) into master (c1b5077) will decrease coverage by 0.13%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1810      +/-   ##
==========================================
- Coverage   58.38%   58.25%   -0.14%     
==========================================
  Files          66       66              
  Lines        6705     6721      +16     
==========================================
  Hits         3915     3915              
- Misses       2790     2806      +16     

Impacted Files	Coverage Δ
tardis/tardis/visualization/tools/sdec_plot.py	9.52% <0.00%> (-0.43%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update c1b5077...786ac89. Read the comment docs.

[jamesgillanders]

Same as previous PR - all looked good then and it is still good now!