feat: search custom filters

[ThibaudDauce]

You can test it on http://dev.local:3000/design/dataset-search

Replace #1034

[abulte]

@ThibaudDauce this looks pretty good, thanks.

Re integration downstream: I'll have a challenge injecting the right filter templates depending on which site is visited. In #1034 it was simply a matter of building a site-aware conf and passing it, now I need dynamic templates somehow (I hope I'll be able to keep everything in config on downstream side at least). BTW, this PR breaks the "everything in config" paradigm we had before.

But I agree it's more powerful and will be able to handle more use cases in the future (which I don't have in mind right now). I'll try to integrate in opendatateam/udata-front-kit#1153 and let you know how that goes.

[abulte]

@ThibaudDauce can you port the styles modifications here?

https://github.com/datagouv/cdata/pull/1034/changes#diff-e8eff0975d30ae4013561b11a589489938009a4fda06462ab26128b2d38761f9
https://github.com/datagouv/cdata/pull/1034/changes#diff-0d57faf320f884f54f042894a1733683cf023426598b2f2710bcd3478da88650

It lets downstream have the style for SearchableSelect 🙏

[ThibaudDauce]

@ThibaudDauce can you port the styles modifications here?

https://github.com/datagouv/cdata/pull/1034/changes#diff-e8eff0975d30ae4013561b11a589489938009a4fda06462ab26128b2d38761f9 https://github.com/datagouv/cdata/pull/1034/changes#diff-0d57faf320f884f54f042894a1733683cf023426598b2f2710bcd3478da88650

It lets downstream have the style for SearchableSelect 🙏

Done in 225c146