[ php ] Add code samples for missing content

[rachfop]

The following sections need code samples.

Provide a code sample per section by using the comment section to provide a code snippet.
Mark the checkbox complete as sample code is added.

If the language does not support a feature, write “NA” or link/code to a related concept: for an example, see Go’s Remove Search Attribute.

Testing

• Assert In Workflow
• Automatic Method
• Cancel An Activity
• Listen To Heartbeats
• Manual Method
• Replay
• Run An Activity
• Setting Up
• Skip Time In Activities
• Test Activities
• Test Frameworks
• Workflow Context

Observability

• Custom Logger
• Logging
• Metrics
• Remove Search Attribute
• Search Attributes
• Tracing
• Visibility

Features

• Mutable Side Effects
• Namespaces
• Side Effects

[roxblnfk]

Documentation drafts that should be moved into documentation site:

• Expose Replayer API sdk-php#336
• Eager Workflow start client option sdk-php#355
• Mentions about UUID, HistoryLength and visibility features from v2.6.0 release may be introduced in the documentation