Add new El Nino tour story

[torimcd]

Description

Fixes #5582

Add new tour story content for understanding recent El Nino events.

How To Test

1. Verify El Nino is added as a tour story
2. Verify all steps behave as expected

PR Submission Checklist

This is simply a reminder of what we are going to look for before merging your code.

• I have read the CONTRIBUTING doc
• I have added necessary documentation (if applicable)
• I have added tests that prove my fix is effective or that my feature works (if applicable)
• Any dependent changes have been merged and published in downstream modules (if applicable)

Merging

Please use the squash and merge commit method unless each commit in your branch is vital to the commit history of main.

@nasa-gibs/worldview

[N1GHTM4R]

Accurate. I feel we should add localization to these.