Update asar website header navbar

[sbreitbart-NOAA]

What is the feature?

• Change asar website header navbar option from "References" to "Example Reports"
• force other options to open in new tabs
• remove non-functional "sourcecode" from structure

How have you implemented the solution?

• Editing pkgdown.yml

Does the PR impact any other area of the project, maybe another repo?

• No

[Schiano-NOAA]

Great improvements! Thanks

[github-actions]

Checklist

• PR base branch is accurate
• Is the code concise?
• Comments are clear and useful.
• Can you remove or combine any arguments?
• Do argument contain defaults (if appliable)?
• Code is documented and example provided (Roxygen).
• Did you make a test (testthat)?
• Was this tested under multiple scenarios?
• Did you run devtools::check()?