PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/docs.nestjs.com/blob/master/CONTRIBUTING.md

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Docs
• Other... Please describe:

What is the current behavior?

The Microservices MQTT transport documentation currently only describes configuring a global subscribeOptions (including qos) for all subscriptions.
It does not mention that QoS can be overridden per pattern/handler.

Issue Number: N/A

What is the new behavior?

The MQTT transport docs now include a small section describing how to override the subscription QoS per pattern/handler using extras.qos.
This showcases the feature added in nestjs/nest and clarifies that:

• when extras.qos is provided, it overrides the QoS for that pattern
• when not provided, the global subscribeOptions remains the default

Does this PR introduce a breaking change?

• Yes
• No

Other information

• Docs updated: content/microservices/mqtt.md
• Related feature PR: feat(microservices): support per-handler qos in mqtt nest#16286