Update default container config to avoid deprecation warning

[donoghuc]

Release notes

The default configuration for logstash container images no longer warns of a deprecated http.host configuration option.

What does this PR do?

Use the api.http.host instead of http.post in the default container config to avoid noisy deprecation warnings.

Why is it important/What is the impact to the user?

Consumers of container will not need to modify the default config to avoid seeing deprecation warnings.

[elasticmachine]

:broken_heart: Build Failed

• Buildkite Build
• Commit: de592dc1e3d6b78cf074bf135777dd8d79cc9c4d

Failed CI Steps

• :lab_coat: Integration Tests - FIPS mode / part 4-of-6
• :lab_coat: Integration Tests - FIPS mode / part 4-of-6
• :lab_coat: Integration Tests - FIPS mode / part 4-of-6
• :lab_coat: Integration Tests - FIPS mode / part 4-of-6
• :lab_coat: Integration Tests / part 4-of-6

[donoghuc]

We need to do a bit more research in to the upgrade/compatability of this change. For example if api.host is set and we introduce this as a default, what will be the outcome? A duplication warning/error? Nothing?