Add sharding key for db/docs/elastic_reindexing_slices.yml
Proposal
See epic for background
- Identify and add a sharding key to the docs YAML, see the documentation
- Determine if the database schema should be
gitlab_main_cell
orgitlab_main_clusterwide
, see the documentation
Note: Most tables should be gitlab_main_cell
as each Cell will have it's own Elasticsearch cluster