Add dev deps.edn in the project root

[PEZ]

Making clojure-lsp serve the whole repository when opened at the root in, say, Calva.

Please provide enough information so that others can review your pull request:

In BetterThanTomorrow/calva#2337 it came to my attention that Calva's clojure-lsp services are not in effect if the repository is opened at its root. The way to solve that is to add a deps.edn at the root to help clojure-lsp figure out the class paths and thus which files to analyze.

Explain the details for making this change. What existing problem does the pull request solve?

Only adding a deps.edn at the root which references the “sub” projects.

Screenshots/GIFs

This only effects development. I could add some screenshots, but don't know if it would bring so much info. 😄

Please let me know if I can clarify this.

[PEZ]

For visibility I paste my comment on #3802 here as well

It could be good to know that it is not Calva config, per se. It is Clojure CLI config, and generally will help any clojure repl started at the project root to figure out the classpath. And it also helps clojure-lsp which uses clojure to assemble the classpath which it needs to know in order to analyze the right files and be able to deliver its services. And Calva integrates clojure-lsp.

Hopefully it helps clarify things I didn't quite clarify in the PR description.

[EvaMarco]

Merged manually, thanks¡¡¡¡