bug: inconsistent usage of topic flags

[jakubgs]

Problem

There's two ways to use topics flags:

• --topics - Takes a list of comma separated topics, CANNOT be repeated.
• --protected-topic - Does NOT take a list, CAN be repeate.

Makes no sense.

Impact

Almost made me vomit.

Expected behavior

Not inducing nauseousness. Probably just make --topics into --topic and allow it to be repeated.

Additional context

nwaku/apps/wakunode2/config.nim

Lines 210 to 213 in b277ce1

	topics* {.
	desc: "Default topics to subscribe to (space separated list)."
	defaultValue: "/waku/2/default-waku/proto"
	name: "topics" .}: string

nwaku/apps/wakunode2/config.nim

Lines 40 to 43 in b277ce1

	protectedTopics* {.
	desc: "Topics and its public key to be used for message validation, topic:pubkey. Argument may be repeated."
	defaultValue: newSeq[ProtectedTopic](0)
	name: "protected-topic" .}: seq[ProtectedTopic]

[jm-clius]

Hahaha. Yeah, this is bad. The --topics config item is old and was never used until recently, so no-one scrutinised how ugly it is against the rest of the config items. I think --topic should be repeated argument (similar to almost all other repeated config items).