feat: prepare ElasticSearch 8

[ThibaudDauce]

Following a report from @estellebertrand, we use 7.17.24 in production. We could revert this change when deploying the 8.19.13 in production. And then 9.3.2 ?

• Revert the ElasticSearch SDK to 7.17.28 to match the production
• Add ElasticSearch 8 to the CI
• Disable action.destructive_requires_name because the cleanup is using * in indices names (not allowed in v8)
• Replace cardinality(_id) by doc_count because "Fielddata access on the _id field is disallowed, you can re-enable it by updating the dynamic cluster setting: indices.id_field_data.enabled"

We use the 7.17 SDK because the CI matrix can't conditionally swap SDK versions per ES version. ES 8 enables security (auth + TLS) by default, which the 7.x SDK doesn't support, so we disable it with xpack.security.enabled: false to allow the old SDK to talk to ES 8 without auth.

When migrating the server to ES 8 in production:

1. Deploy ES 8 with security disabled
2. Upgrade the SDK to 8.x with auth support configured
3. Re-enable security on the server