Enhancement/issue 435 deeply nested relative paths

[thescientist13]

Related Issue

resolves #435

See for an example / reference - thegreenhouseio/www.thegreenhouse.io#215

Summary of Changes

1. Added support for using relative paths ../ in templates for CSS / JS no matter the level of page nesting
2. Refactored some common URL calculation methods into ResourceInterface
3. Added test cases specifically for deeply nested pages and all relative path usage
4. Updated website to use ../ consistently

TODO

1. Update template docs recommendations accordingly (note: using absolution (/) is probably going to be marginally faster, fyi)
2. Update consolidate all Greenwood standard plugin usage into one place #520 to have plugin-user-workspace defer resolution if another plugin "claims" to resolve (e.g. like node_modules instead of testing for it specifically)
3. Noticed we are including our fonts twice; in app.html and theme.css. (app.html already includes theme.css). Will open a separate PR for this. - remove duplicate load of css font #619
4. Fix Windows CI
5. fix package.json loading on Windows - is its own issue not related to this PR import JSON via ESM for the website is not bundling correctly on Windows #620
6. investigate local mono repo packages work around
7. test front matter imports
8. Make discussion around symlink work around for Greenwood development in rollup.config.js - remove local development symlink workaround from rollup.config.js #623