Add optimization profiles to Elasticsearch Serverless billing

[lcawl]

Relates to https://github.com/elastic/cloud/issues/146427

This PR updates https://www.elastic.co/docs/deploy-manage/cloud-organization/billing/elasticsearch-billing-dimensions with information about the impact of the optimized_for value.

It must not be merged until the related changes to the default behaviour occur.

[github-actions]

🔍 Preview links for changed docs

• deploy-manage/cloud-organization/billing/elasticsearch-billing-dimensions.md

[petegaleotti]

• Project subtype or profile: When you use the API to create projects, be aware that the optimized_for option affects the VCU usage and costs.

I recommend rewording this to "...option affects VCU allocation and costs."

The vector option is recommended only for uncompressed dense vectors (dense_vector fields with int4 or int8 quantization strategies) and high dimensionality. Though the per VCU cost is the same for general purpose and vector profiles, the latter provides a larger amount of RAM for searchable data. This leads to higher VCU consumption in order to improve the performance for uncompressed vector data.

I recommend rewording this with, "...the latter allocates more VCUs for searchable data. This leads to...".

[kilfoyle]

LGTM! 🐰