I never used CDN source in my CRM web resource developments. Always have a local copy uploaded in CRM as web resource to refer in HTML pages and checked into Azure DevOps as well. I never faced any issues in this approach. I remember CDN url broke like you said when I tried last time.
Just sharing the url paths from <head>
section that I'm using in one of my HTML web resource.
<script src="mts_jquery/2.1.4/jquery.min.js"></script>
<script src="mts_typeahead.bundle.js"></script>
<script src="mts_bootstrap/3.3.5/bootstrap.min.js"></script>
<link href="mts_bootstrap/3.3.5/bootstrap.min.css" rel="stylesheet" />
<link href="mts_bootstrap/3.3.5/bootstrap-theme.min.css" rel="stylesheet" />
<script src="mts_bootstrap-tagsinput.js"></script>
<link href="mts_bootstrap-tagsinput.css" rel="stylesheet" />
