Add downsampling_method to the data stream lifecycle

[gmarouli]

In elastic/elasticsearch#137023 we add the sampling method also in the data stream lifecycle.

This first two commits of this PR do the following:

• Fixes the API, the first commit is extracted to Fix data stream lifecycle type, to correctly handle downsampling. #5593 so it can be properly backported.
• Adding the downsampling method to the data stream lifecycle and the data stream lifecycle request.

This PR is work in progress until #5593 is validated an merged.

[github-actions]

Following you can find the validation changes against the target branch for the APIs.

API	Status	Request	Response
cluster.get_component_template	🔴 → 🟢	15/15	14/15 → 15/15
cluster.put_component_template	🔴	33/38 → 34/38	38/38
indices.get_index_template	🔴 → 🟢	24/24	23/24 → 24/24
indices.put_data_lifecycle	🔴 → 🟢	6/7 → 7/7	7/7
indices.put_index_template	🔴	146/171 → 147/171	171/171

You can validate these APIs yourself by using the make validate target.

[nielsbauman]

These changes also LGTM :)

[pquentin]

Thanks! LGTM.