fix(webserver): allow label value containing a comma

[yuri1969]

What changes are being made and why?

Queries like ?labels=foo:bar,baz failed since due using , as the default query param separator. The baz value was attempted to be parsed as a label.

This PR switches the labels parameter format from param=Mike,Adam,Kate to param=Mike&param=Adam&param=Kate. More details in: Micronaut - Customizing Parameter Binding

Note, the changed param format might be a breaking change for API clients.

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How the changes have been QAed?

Create a new execution with label named foo of value bar,baz using the UI.