Feature flat index

[cmark]

This is a repository synchronization PR up to the tag v5.0.0-alpha in b2i/snow-owl.

The PR contains the following changes from b2i/snow-owl:

• All changes up to 4.6.0 release (branch queueing converted back to sync mode for compatibility)
• Changes from 4.7.0 release except the extension management feature
• Flat index support from 5.0.0

Changes made to the following IHTSDO/snow-owl only services after the merge:

• MRCM Rest Service getPredicates() uses both the inferred and stated hierarchy
• Due to removal of SnomedTerminologyBrowser, client terminology browsers are currently unsupported and may not work until 5.0.0 is released. Therefore we've changed Authoring Normal Form generator code to use the SNOMED CT Request based APIs instead. This is a one-one conversion from the old to the new API, and the result might be suboptimal compared to the original.
• ClassificationRun and MergeReview indexes still use the old index API, data migration is not required
• Moved MergeReviewManager implementation out of ReviewManagerImpl
• Bumped version to 4.6.0-SNAPSHOT.

Related documentation:

• CHANGELOG.md
• No 4.x -> 5.0 migration guide yet (see the snowowl reindex command in the Admin Console Reference)

The corresponding Merge Request for the SCA is https://git.ihtsdotools.org/ihtsdo/snowowl-rest-api-updates/merge_requests/18.

[kaicode]

We are provisioning a machine to test the data migration and full regression test using this feature.

[cmark]

:+1:

[apeteri]

Changes in the feature branch (including performance counters) were merged to develop.