This PR adds functionality to search by a global search prefix.
This allows Mattermost to be used across multiple data centers
with multiple Elasticsearch instances synchronized using
cross-cluster replication.
While here, we also add tests cases to cover for some missing
search interface methods.
For now, no system console setting is exposed. Because IndexPrefix
is also not exposed. It can be added later if a need arises.
https://mattermost.atlassian.net/browse/MM-63298
```release-note
A new config setting ElasticsearchSettings.GlobalSearchPrefix is added
which can be used to search across multiple indices having a common prefix.
This is useful in a scenario with multiple Elasticsearch instances, where
multiple instances are writing to different indices with different prefixes
using the ElasticsearchSettings.IndexPrefix setting.
```
Co-authored-by: Mattermost Build <build@mattermost.com>
We add a new field delete_at in the channels template.
This field is then searched in the SearchChannels function.
Also added tests to verify that archived channels are searched
properly, and also indexed correctly.
https://mattermost.atlassian.net/browse/MM-62295
```release-note
- Now archived channels are searchable with ES/OS if TeamSettings.ExperimentalViewArchivedChannels is enabled.
- If there are old channels which were archived before a bulk index was run, users would need to purge indexes, and do bulk index again. Because those old archived channels are removed from the index when a bulk index is run.
```
Co-authored-by: Mattermost Build <build@mattermost.com>
