`flagtools.transferFlags` vs. `resampling.concatFlags`

We now have to functions to transfer flags/histories from one variable to another:

1. The rather new flagtools.transferFlags which adds flags from source to target. This is only a wrapper around generic.flagGeneric and therefore has the same limitations (source and target need to have the same index).
2. The older and more powerful , func=isflagged(K25_)), which adds the history from source to target and also allows for some sort of resampling.

IDK, for me this seems to be redundant and I wonder, if we should merge both functionalities into one function. I would suggest the following:

1. Extend resampling.concatFlags with:
   • a default to method and suggest "match"
   • another parameter like squueze: bool=Truewhich determines if the entire history of just the flags should be concatenated
2. Make flagtools.transferFlags a wrapper around resampling.concatFlags
3. Optionally: deprecate flagtools.transferFlags in 2.1 and remove it in 2.2 or 2.3.

What do you think @palmb and @luenensc ?