[ 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:

• [x] https://github.com/temporalio/sdk-php/pull/336
• [ ] https://github.com/temporalio/sdk-php/pull/355
• [ ] Mentions about UUID, HistoryLength and visibility features from v2.6.0 release may be introduced in the documentation