Update the indenter to handle the cljfmt 0.11.x breaking config update since version 2.0.383

[PEZ]

From https://github.com/weavejester/cljfmt/tree/master#breaking-changes-in-011x:

The :indents key has been split into :indents and :extra-indents. The :indents key replaces all default indents, while the :extra-indents key will append to the default indents.

This probably should be mentioned in the Calva docs. Perhaps it calls for an update to the docs more generally to include the :extra-indents, since that is probably the most common configuration from now on.

It also calls for an update of how the Calva indenter reads the configuration. We probably need to recreate the logic now used in cljfmt for this, including the :legacy/merge-indents? escape hatch.