elasticsearch: Switch from LZ4 to DEFLATE compression

What does this MR do?

Alters the index settings so that new indexes will use a more efficient compression algorithm. This trades space for time, as is always the way.

Existing indexes are not automatically updated, but there is no incompatibility with them. We can update this setting on-the-fly for existing indexes - and maybe we should add a rake task that will do this - but since it will be useful for other settings, and the implications need to be throught through, I'd rather spin off a follow-up issue for this if we deem it potentially worthwhile.

What are the relevant issue numbers?

Closes #10420 (closed)

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