Add GitHub Action Workflow for Updating Upstream components

[coatless]

The idea behind this is to setup a workflow that automatically:

• Checks if a new version of the upstream library has been released.
• Downloads and extracts the new version of the library
• Updates version in DESCRIPTION
• Adds new entry in ChangeLog
• Update the NEWS.md file with information from HISTORY.md and include/ensmallen_bits/ens_version.hpp automatically.
• Creates a new PR with the changes for final review

This uses heavily modified version of an upstream workflow action described at:

• https://stackoverflow.com/questions/58465057/trigger-a-github-action-when-another-repository-creates-a-new-release
• https://github.com/peter-evans/create-pull-request/blob/master/docs/examples.md#update-swaggerui-for-github-pages

The main difference between both approaches is we use the embedded ensmallen version file to create a version string instead of maintaining a separate file in the repository that stores the version. Version information for the embedded ensmallen file is extracted using regular expressions using three different grep statements as I opted to avoid making a bash array. Additionally, there was work put into ensure the correct format for updating ChangeLog and NEWS.md.