Fix #234, Documentation and Guides Workflow Run on All Push Events

[ArielSAdamsNASA]

Checklist (Please check before submitting)

• I reviewed the Contributing Guide.
• I signed and emailed the appropriate Contributor License agreement to GSFC-SoftwareRelease@mail.nasa.gov and copied cfs-program@lists.nasa.gov.

Describe the contribution
Fixes #234

• Removed the main branch for push so that the workflow runs on all branches for push and pull requests.
• Added the duplicate jobs action so that the workflow does not run any duplicate jobs.

Testing performed
Tested locally

Expected behavior changes

• The Documentation and Guides workflow should run on all push events. For example, when users push code to their forked repos, the Documentation and Guides workflow should run.
• When a user pushes code to a pull request, the workflow should not run duplicate jobs for both push and pull requests.

Contributor Info - All information REQUIRED for consideration of pull request
Ariel Adams, ASRC Federal

[astrogeco]

CCB:2021-04-07 APPROVED