Add cost-analysis documentation

[NipunFernando]

Purpose

Add Choreo Cost Optimization feature documentation under Insights > Cost Insights.

Resolves https://github.com/wso2-enterprise/choreo/issues/34221

Related Epic

https://github.com/wso2-enterprise/choreo/issues/31288

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1 out of 2 committers have signed the CLA.

✅ NipunFernando
❌ Adeepa Fernando

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[tishan89]

File path should change. Currently it is
en/developer-docs/docs/monitoring-and-insights/cost-optimization/cost-optimizatio.md

We do not need a folder if it is just one doc.
There is a typo in file name
Lets highlight where we say about the this is just this months data(Bold)

[NipunFernando]

File path should change. Currently it is en/developer-docs/docs/monitoring-and-insights/cost-optimization/cost-optimizatio.md

We do not need a folder if it is just one doc. There is a typo in file name Lets highlight where we say about the this is just this months data(Bold)

Done.