Consider links between tools and related resources

[greatislander]

Is your feature request related to a problem? Please describe.

As in platform-coop-toolkit/coop-map-directory-index#10, we should consider ways we can connect tools to related resources (e.g. case studies) in the Resource Library.

Describe the solution you'd like

API endpoint in the Resource Library allows us to query for resources related to a given tool.

Describe alternatives you've considered

Not applicable.

Additional context

Not applicable.