ENH: Solution for issue #39859 | Added documentation source link to each page

[ADing4818]

• closes DOC: add button to edit on GitHub #39859
• Had manual testing with url paths on local machine to make sure the url splicing worked properly. Also tested the pandas code in a docker container to make sure that the source links for the documentation showed up consistently on each page.
• The file that was edited was "doc/_templates/sidebar-nav-bs.html" - please review this file. When I committed, just to be safe, I did "git add -A", but the only file that was edited was the nav-bs.html file.