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>
We cannot simply use Elasticsearch any more because
we support Opensearch as well.
Therefore changing Elasticsearch to just say Search.
Note: There are still some cases where Elasticsearch
is used. That is intentional and necessary.
```release-note
NONE
```
After https://github.com/mattermost/mattermost/pull/29209, there were some more
strings which were left out. Sending another PR to fix all of them.
The config validation strings are made generic for simplicity, because they
are called before the search backend is started, and even though you could
check for the config setting, it forces the code order. Therefore, changed
the words to just say "Search" for simplicity.
I tried to use Aider initially for a little while, but ended up fighting
a lot with the search/replace and having to repeat myself over and over again
to get it to do the refactoring. Eventually gave up and did rest of the changes
myself.
```release-note
NONE
```
