[RUM-8700] Support for Account Information on all Datadog products

[Valpertui]

What and why?

Add support for the Account field in Datadog data model. Account let you to identify the account related to the current usage session of the host application.
The definition of what an account is, is flexible and is up to you and your business needs. Account information is propagated across the entire stack of Datadog products: RUM, Logs, Traces, Crash Reporting...

How?

Review checklist

• [x] Feature or bugfix MUST have appropriate tests (unit, integration)
• [x] Make sure each commit and the PR mention the Issue number or JIRA reference
• [x] Add CHANGELOG entry for user facing changes
• [x] Add Objective-C interface for public APIs (see our guidelines [internal]) and run make api-surface)

[datadog-datadog-prod-us1[bot]]

Datadog Report

Branch report: valpertui/RUM-8700/add-setAccountInfo Commit report: edff202 Test service: dd-sdk-ios

:white_check_mark: 0 Failed, 2531 Passed, 1357 Skipped, 3m 24.46s Total duration (1m 45.81s time saved)

[shagedorn]

The definition of what an account is, is flexible and is up to you and your business needs.

Can you share some more motivation on adding this API, especially in contrast to using setUserInfo(…)? Do you have an example where one would use setAccountInfo(…) instead of (or in addition to) setUserInfo(…)?