Increase UT code coverage to 72% from baseline of 65%

[mehuled]

package/files good to have increased code coverage for

• filtering/as-filter.go
• worker/service.go
• openapi-server/service.go
• messagebroker/tracing.go
• messagebroker/kafka.go

packages to be excluded from UT test coverage

• messagebroker/pulsar.go

[mehuled]

@vnktram can you please add additional packages that we can improve UTs on?