RUM-14055 Remove ResponseSize from addResourceMetrics API

[barboraplasovska]

What does this PR do?

In this PR on dd-sdk-ios we remove responseSize and add

requestBodySize: (encoded: Int64, decoded: Int64)? = nil,
responseBodySize: (encoded: Int64, decoded: Int64)? = nil

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests
• Make sure you discussed the feature or bugfix with the maintaining team in an Issue
• Make sure each commit and the PR mention the Issue number (cf the CONTRIBUTING doc)
• If this PR is auto-generated, please make sure also to manually update the code related to the change

[cdn34dd]

This should be fine, just make sure to update the failing tests.