Add support for multilines mappings in backport_records

[leplatrem]

mozilla/remote-settings#733

[alexcottner]

This is better (obviously). But it still means we need N rows of config for each collection we're copying to. Is it possible for us to support a little regex in here so as the collection grows we don't have to keep making changes? Ex:

main\/shops\?contains_regions=\["(\w+)"\] -> main-workspace/shops-$1

[alexcottner]

I have a suggestion that could make this better (or at least let us update it less often). But this is still a good improvement so approving.

[leplatrem]

But it still means we need N rows of config for each collection we're copying to. Is it possible for us to support a little regex in here so as the collection grows we don't have to keep making changes? Ex:

With the regexp approach, I don't understand how do you define the inputs.
The goal of this is not to breakdown automatically for each possible field value, but copy a subset of records from one source collection to another. We don't necessarily want a collection for each possible value (ex. bid/cid?country=us -> bid/cid-us, bid/cid?not_country=us -> bid/cid-world).

We sort of touched that topic in https://github.com/mozilla/remote-settings/pull/729/files#r1910743449