RUM-7435: Add Session Replay startRecordingImmediately ObjC API

[0xnm]

What and why?

This PR adds missing Session Replay startRecordingImmediately ObjC API.

Review checklist

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

[0xnm]

/merge

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2024-11-26 09:08:45 UTC ℹ️ MergeQueue: waiting for PR to be ready

This merge request is not mergeable yet, because of pending checks/missing approvals. It will be added to the queue as soon as checks pass and/or get approvals.
Note: if you pushed new commits since the last approval, you may need additional approval.
You can remove it from the waiting list with /remove command.

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2024-11-26 10:00:44 UTC ℹ️ MergeQueue: merge request added to the queue

The median merge time in develop is 27m.

[datadog-datadog-prod-us1]

Datadog Report

Branch report: nogorodnikov/rum-7435/add-session-replay-startrecordingimmediately-objc-api
Commit report: 974910c
Test service: dd-sdk-ios

✅ 0 Failed, 3554 Passed, 0 Skipped, 3m 43.67s Total Time
🔻 Test Sessions change in coverage: 3 decreased, 3 increased, 8 no change

🔻 Code Coverage Decreases vs Default Branch (3)

• test DatadogInternalTests tvOS 80.4% (-0.02%) - Details
• test DatadogCrashReportingTests iOS 26.63% (-0.02%) - Details
• test DatadogInternalTests iOS 80.38% (-0.02%) - Details