Ability to import saved object files larger than 10MB

[mikecote]

With the new server side import API, there is a limit of 10MB the server will accept. As discovered when testing #34896, we need the UI to display a proper error when the limit is reached instead of The file could not be processed. as well as increase the limit in order to be able to import / export a larger amount of canvas objects.

[elasticmachine]

Pinging @elastic/kibana-platform

[cqliu1]

Canvas has the workpad size limit set to 25MB, so it'd be nice if we could raise the limit to 25 in case users try to import a large workpad.

[rudolf]

#66387 is tracking displaying the error message in the UI. We have savedObjects.maxImportPayloadBytes setting which can be used to increase the limit. Increasing the limit can open up for a malicious actor sending a large payload which consumes a lot of memory. But we can increase the default to ~25MB if we think users will regularly bump into this problem.