Indicate which string fields/options are multibase

## Problem

https://github.com/ipfs/go-ipfs/pull/8183 introduced a breaking change where pubsub topic name is expected to be a multibase string, but the type of the field remains to be `string`.

[ipfs-docs/http-api-docs](https://github.com/ipfs/ipfs-docs/tree/main/tools/http-api-docs) reads go-ipfs sources and generates docs like https://docs.ipfs.io/reference/http/api/#api-v0-pubsub-sub which are EXTRA confusing – reader may asume those are strings in cleartext, not bytes represented as multibase (that usually happen to be a valid string):

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## Solution

Find a way to indicate those fields are multibase (new type? additional metadata?), and then update [ipfs-docs/http-api-docs](https://github.com/ipfs/ipfs-docs/tree/main/tools/http-api-docs) to surface that info in produced HTML.

Read the go-ipfs command and option definitions that ipfs-docs/http-api-docs consumes, then inspect how that tool generates the HTTP API HTML. Determine how multibase information can be represented and surfaced without treating these values as ordinary strings. Done means the affected fields are identified in generated documentation and the representation is supported across both repositories.

Written by the indexing model from the issue text.