Supported Highlighting in Elasticsearch

[SjSnowball]

PR for Support Highlighting feature in Elasticsearch #1872

Proposed changes:
Added code to push the highlighted results to meta_data results

Status (please check what you already did):

• First draft (up for discussions & feedback)
• Final code
• Added tests
• Updated documentation

[bogdankostic]

Hi @Sj-Snowball, thank you very much for your contribution! :)
@tstadel will have a look at it at the beginning of next year.

[tstadel]

Hey @SjSnowball,
cool to have your PR. I added some comments. Most of them are minor changes. However, I think we should copy over the whole "highlight" entry into our meta_data and add some remarks where you can find the highlights if you set a custom_query with highlighting to the ElasticsearchRetriever docstrings. To emphasize that this is not a normal meta_data field, we might call it "highlighted". But I leave that up to you as "highlight" might be more intuitive to most (elastic search) users.

[ZanSara]

Hello @Sj-Snowball, just checking if you will have time to work on this PR in the next days. If not, just let us know so we can apply the necessary changes and merge it before it gets too much out of sync with master 🙂

[CLAassistant]

All committers have signed the CLA.

[SjSnowball]

@tstadel Have made the changes

[Timoeller]

Hey @SjSnowball. Thanks for the contribution. Our contributor license bot identified it as a significant contribution for which we require a contributor license agreement. For more info on this please have a look at: https://github.com/deepset-ai/haystack/blob/master/CONTRIBUTING.md#contributor-licence-agreement-cla
Could you sign the CLA please before merging this improvement?

[tstadel]

I just added a usage example to the ElasticsearchRetriever and ElasticsearchDocumentStore docstrings.

[tstadel]

The changes look good to me, @SjSnowball. As soon as you sign the CLA we are good to merge :-)

[Timoeller]

Sorry, I can confirm that user "SjSnowball" has signed the CLA this morning. But the assistant is complaining about "Sj-Snowball" with a hyphen. And also this user created the commits.

Did you by any chance change your github name recently?
Edit: I found https://github.com/Sj-Snowball which you apparently used for creating initial commits.

Anyways, I made the assistant pass the check also for "Sj-Snowball". Lets re-trigger the check

[Timoeller]

Ok ready to roll! :D