Don't load global state when only restoring indices

[ywelsch]

Restoring from a snapshot currently also always loads the global state (templates, customs, ...) even though it's not always used by the restore process, for example when include_global_state is set to false in the restore request. In case there are version incompatibilities in the global state file, or corruption issues, this prevents indices from being restored. We could instead simply not load the global state when it's not required for the restore process.

/cc: @elastic/es-distributed

[bleskes]

Seems logical to me. @tlrx , any opinions?

[tlrx]

We could instead simply not load the global state when it's not required for the restore process.

It makes sense to me. I think that we can have the same issue when deleting a snapshot but I'm not sure we can avoid loading the global state in this case. I'll take a look.