document-database

See #1029

Is your feature request related to a problem? Please describe.
CSV files produced in different locales have different default separators, a comma-separated file (",") is but one type of CSV.

In Sweden we usually use a semicolon (";") as separator and many CSV files use a tab as separator ("\t"). Importing CSVs requires reformatting them before import, and causes inoperability issues and f

Right now in insertElementRecursive(), DocLayer does NOT try to store arrays with null values as sparse arrays, i.e. for null value it still insert a k-v for it, which is kind of against what it attempts to achieve later when doing update (skipping the null values and effectively store those arrays as spars arrays). We should make the behavior consistent and do the same in insertion.

{testthat} 3.0.0 was released in October 2020, and some functionality {uptasticsearch} uses from it is now considered deprecated.

From the {testthat} vignettes on v3.x (link), the following are deprecated and may be removed in a future major release:

• `testthat::context(