feat(catalogue): As a researcher I want to download filtered searches as a .csv file

[timcadman]

Is your feature request related to a problem? Please describe.
The main goal of a researcher using the catalogue is to identify which variables and cohorts are available for a planned analysis. The filters available within the variable and cohort views are very useful for this goal, however there is no easy way to export this information.

Describe the solution you'd like
The option to download search results as .csv files. This should include within the variables page both the 'list of variables' and 'harmonisations' pages, and searches within the 'cohorts' page.

Describe alternatives you've considered
Currently the work around is to try to copy and paste from the browser, which is very messy.

Additional context
Request from end user from IHEN project

[mswertz]

I suppose we should have this for both 'variables' and 'collections' list.

Indeed not immediately straightforward.
It is easy to export variable lists, so we could link to that feature here https://data-catalogue.molgeniscloud.org/catalogue/tables/#/Variables

But I suppose we would like to include existing of mappings to the cohorts, that would require a custom report.