Add index mode to get data stream API (#122486)
This commit adds the `index_mode` for both the data stream and each
backing index to the output of `GET /_data_stream`. An example looks
like:
```
{
"data_streams" : [
{
"name" : "foo-things",
"indices" : [
{
"index_name" : ".ds-foo-things-2025.02.13-000001",
...
"index_mode" : "standard"
}
],
...
"index_mode" : "standard"
},
{
"name" : "logs-foo-bar",
"indices" : [
{
"index_name" : ".ds-logs-foo-bar-2025.02.13-000001",
...
"index_mode" : "logsdb"
},
{
"index_name" : ".ds-logs-foo-bar-2025.02.13-000002",
...
"index_mode" : "logsdb"
}
],
...
"index_mode" : "logsdb",
}
]
}
```
47706b505f