Replaces `composable index template` and `composable template` with
`index template` throughout data stream-related docs.
`Composable index template` is only used to contrast with legacy index
templates.
Limit the creation of data streams only for namespaces that have a composable template with a data stream definition.
This way we ensure that mappings/settings have been specified and will be used at data stream creation and data stream rollover.
Also remove `timestamp_field` parameter from create data stream request and
let the create data stream api resolve the timestamp field
from the data stream definition snippet inside a composable template.
Relates to #53100
