Parse and validate mappings in index templates when they are put

[synhershko]

Currently, putting a template will succeed if the JSON is valid even if the mapping couldn't be parsed. An error will be thrown when the index will be created and try to use the mapping, but that may be too late.

An example for such an error is described in #2414

The probable solution is to validate the mapping defined in the template when putting it.

[spinscale]

Hey,

I absolutely agree we should have better error handling in that case. Do you have any other samples except the date format where this happens in templates?

[synhershko]

Not at the moment. I assume analyzer names and various configuration options?

[clintongormley]

I think all of these are now handled correctly. Please open a new issue if you find another problem.

[johtani]

related #8695
now, we have mappings validation when we create index. no validation when create template.