feat: convert SDK output to module

[kanadgupta]

🧰 Changes

Quick overview of what this PR does:

• Adds the "type": "module" field to the package.json file in the codgen'd SDKs
• Updates our exports entrypoints in the codegen'd SDKs accordingly
• Adds .js file extensions to all of the relative file imports in the codegen'd TS files

I opened this PR in hopes of fixing the typing issues in RM-8230 (which I later determined were an issue with my test environment and not with these SDKs)... but I still think our codegen'd SDKs should incorporate these changes! Here's why:

• ESM is the future and we should probably be using that as the default
• Since we're already requiring modern Node/TS anyways, this has zero impact for CommonJS users
• The .js convention for relative file imports feels safer and more future-proof, even if tsup is proactively handling that for us
• With the --experimental-detect-module flag that has arrived in Node v21, we should be specifying the package.json type value anyways and it feels dated to specify commonjs there

🧬 QA & Testing

Do tests still pass?