[PROPOSAL] Adopt style guide / lint tools code

[dblock]

What/Why

What are you proposing?

I was trying to add some TypeScript code and started typing camelCase methods. Then I noticed that we have adopted of a Ruby-formatting/style in tools such as https://github.com/opensearch-project/opensearch-api-specification/blob/main/tools/merger/OpenApiMerger.ts with snake_case methods and ClassNames. This was probably intended. I propose we codify this, adopt a specific/default TypeScript style guide, and add a linter for it.

What users have asked for this feature?

Future contributors.

What problems are you trying to solve?

Introduce some rules before someone like myself contributes code that looks different.

What is the developer experience going to be?

CI will fail if contribution doesn't fit the style guide and linter doesn't pass.

[nhtruong]

I'm bias for spending years writing Ruby code, but I find snake_case for method names a lot more readable, especially on longer names. Even though the tools are written in TypeScript, where CamelCase is the convention, I'd still vote for snake_case.