debug should use existing containerPort definitions in selecting debug port

[briandealwis]

debug currently selects a port that is as close to the default used by each language runtime's debugger. We should examine the container's containerPorts for an existing definition and use that port if found.

. The Kubernetes API defines the containerPort.name as being IANA_SVC_NAME, and must be unique within the pod. A service name is defined in RFC 6335 as:

Valid service names are hereby normatively defined as follows:

• MUST be at least 1 character and no more than 15 characters long
• MUST contain only US-ASCII [ANSI.X3.4-1986] letters 'A' - 'Z' and 'a' - 'z', digits '0' - '9', and hyphens ('-', ASCII 0x2D or decimal 45)
• MUST contain at least one letter ('A' - 'Z' or 'a' - 'z')
• MUST NOT begin or end with a hyphen
• hyphens MUST NOT be adjacent to other hyphens

As containers within a pod must have unique port names, we should use the debug protocol as a prefix (e.g., look for something matching jdwp(-.+)?).

Motivated by discsussion in #4419.