Feature: Multilingual support - Add request language middleware

[syphax-bouazzouni]

Require

• https://github.com/ncbo/ontologies_linked_data/pull/199

Context

This PR adds a middleware request_lang that will save for each request the parameter lang or language if set, as a global variable that will filter the values by it.

In addition, it updates the search helper, to add the selected language as a suffix of the SOLR requests, to search by the selected language only.

Changes

• Add again SOLR config file as changed for the multilingual support (https://github.com/ncbo/ontologies_api/pull/148/commits/75b05fe7579f7358860f9395a45302e70923995c)
• Add request lang middleware to save as a global variable the request parameter "lang" or "language"(https://github.com/ncbo/ontologies_api/pull/148/commits/9435c7efb50b69ebfb5496a5a50d5b40c28a670d)
• Update the search helper to add as a suffix the selected language (https://github.com/ncbo/ontologies_api/pull/148/commits/f7eaf98320687e2c14c1bf8050de26d58f9c25db)
• Refactor test to be faster by doing the indexation only if needed (https://github.com/ncbo/ontologies_api/pull/148/commits/b5360d242d26c4f216f72cfe688b462a732e489f)
• Add multilingual search unit tests (https://github.com/ncbo/ontologies_api/pull/148/commits/84f079ef8464b9c0e9916d344cbb30ad136b3f57)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 73.28%. Comparing base (f439e21) to head (88973e9).

:exclamation: Current head 88973e9 differs from pull request most recent head 2a675bb. Consider uploading reports for the commit 2a675bb to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #148 +/- ## =========================================== + Coverage 73.13% 73.28% +0.15% =========================================== Files 52 53 +1 Lines 2903 2916 +13 =========================================== + Hits 2123 2137 +14 + Misses 780 779 -1 ``` | [Flag](https://app.codecov.io/gh/ncbo/ontologies_api/pull/148/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ncbo) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/ncbo/ontologies_api/pull/148/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ncbo) | `73.28% <100.00%> (+0.15%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ncbo#carryforward-flags-in-the-pull-request-comment) to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[alexskr]

I understand why the Solr schema was added to the ontologies_api project in this PR; it eliminates the need to keep the ontoportal/solr-ut image synchronized when schema changes occur. A more elegant solution could be implemented to maintain schema synchronization between ontologies_api and ontologies_linked_data, but this requirement will disappear after the schemaless Solr feature is implemented. At that point, the Solr configuration could be removed from ontologies_api.