feat: add Kobiton as a device provider

[sushmakannedari05]

Adds Kobiton as a supported device provider in Appwright, alongside the existing BrowserStack and LambdaTest integrations.

Changes
src/providers/kobiton/index.ts - KobitonDeviceProvider class implementing the DeviceProvider interface
src/providers/kobiton/utils.ts - getAuthHeader() helper using KOBITON_USERNAME / KOBITON_API_KEY
src/providers/index.ts - registered "kobiton" in the provider switch
src/types/index.ts - added KobitonConfig type and included it in the DeviceConfig union
docs/config.md - documented Kobiton provider and required env vars
README.md - added Kobiton to the provider list and sample config
Testing
Android - tested end-to-end on real Kobiton device (Galaxy S22, Android 16) - app upload, session creation, Wikipedia test passing
iOS - code path is identical to Android but not run end-to-end as the sample wikipedia_ios.zip is a simulator build; real device testing requires a signed .ipa
Notes
App upload uses Kobiton's 3-step S3 flow: POST /apps/uploadUrl -> PUT to S3 -> POST /apps
buildPath accepts either a local file path (auto-uploads) or kobiton-store:v{versionId} to skip upload

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Latest commit: 8ffeda7

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