[#2606] Lazy load synonyms for Elasticsearch

[pi-sigma]

The synonyms for Elastic Search need to be loaded after all the migrations have been run.

Taiga: issue #2606

[pi-sigma]

Some thoughts:

• Wrapping load_synonyms in lazy doesn't work (without further ado) because it causes a SerializationError
• We played with the idea of loading synonyms in the ready function and patch ProductDocument, but the solution is neither pretty nor straightforward.

[swrichards]

Some thoughts:

* Wrapping `load_synonyms` in `lazy` doesn't work (without further ado) because it causes a `SerializationError`

* We played with the idea of loading synonyms in the `ready` function and patch `ProductDocument`, but the solution is neither pretty nor straightforward.

Just to add to this: when @alextreme is back we might want to discuss whether this approach is viable at all. There does not appear to be any good way to load synonyms from a Django model (which can only work post-django setup) to be passed into the Document definition (which happens pre-django setup), without doing some ugly monkey-patching.