feat: enable listing API methods for Boost

[LexLuthr]

Fixes #1416

Sample output:

# curl -s  http://boost:1288/rpc/v0 -H "Authorization: Bearer $(cat /var/lib/boost/token)" -X POST -H "Content-Type: application/json" --data '{"method":"Filecoin.Discover","params":[],"id":1,"jsonrpc":"2.0"}' | jq . | head -20
{
  "jsonrpc": "2.0",
  "result": {
    "info": {
      "title": "Boost RPC API",
      "version": "1.7.3-rc1"
    },
    "methods": [
      {
        "deprecated": false,
        "description": "```go\nfunc (s *BoostStruct) ActorSectorSize(p0 context.Context, p1 address.Address) (abi.SectorSize, error) {\n\tif s.Internal.ActorSectorSize == nil {\n\t\treturn *new(abi.SectorSize), ErrNotSupported\n\t}\n\treturn s.Internal.ActorSectorSize(p0, p1)\n}\n```",
        "externalDocs": {
          "description": "Github remote link",
          "url": "https://github.com/filecoin-project/boost/blob/master/api/proxy_gen.go#L271"
        },
        "name": "Filecoin.ActorSectorSize",
        "paramStructure": "by-position",
        "params": [
          {
            "deprecated": false,

# curl -s  http://boost:1288/rpc/v0 -H "Authorization: Bearer $(cat /var/lib/boost/token)" -X POST -H "Content-Type: application/json" --data '{"method":"rpc.discover","params":[],"id":1,"jsonrpc":"2.0"}' | jq . | head -20
{
  "jsonrpc": "2.0",
  "result": {
    "info": {
      "title": "Boost RPC API",
      "version": "1.7.3-rc1"
    },
    "methods": [
      {
        "deprecated": false,
        "description": "```go\nfunc (s *BoostStruct) ActorSectorSize(p0 context.Context, p1 address.Address) (abi.SectorSize, error) {\n\tif s.Internal.ActorSectorSize == nil {\n\t\treturn *new(abi.SectorSize), ErrNotSupported\n\t}\n\treturn s.Internal.ActorSectorSize(p0, p1)\n}\n```",
        "externalDocs": {
          "description": "Github remote link",
          "url": "https://github.com/filecoin-project/boost/blob/master/api/proxy_gen.go#L271"
        },
        "name": "Filecoin.ActorSectorSize",
        "paramStructure": "by-position",
        "params": [
          {
            "deprecated": false,