This PR introduces the /v1/search/fuzzy API endpoint, used for fuzzy
searching objects in Nomad. The fuzzy search endpoint routes requests
to the Nomad Server leader, which implements the Search.FuzzySearch RPC
method.

Requests to the fuzzy search API are based on the api.FuzzySearchRequest
object, e.g.

{
  "Text": "ed",
  "Context": "all"
}

Responses from the fuzzy search API are based on the api.FuzzySearchResponse
object, e.g.

{
  "Index": 27,
  "KnownLeader": true,
  "LastContact": 0,
  "Matches": {
    "tasks": [
      {
        "ID": "redis",
        "Scope": [
          "default",
          "example",
          "cache"
        ]
      }
    ],
    "evals": [],
    "deployment": [],
    "volumes": [],
    "scaling_policy": [],
    "images": [
      {
        "ID": "redis:3.2",
        "Scope": [
          "default",
          "example",
          "cache",
          "redis"
        ]
      }
    ]
  },
  "Truncations": {
    "volumes": false,
    "scaling_policy": false,
    "evals": false,
    "deployment": false
  }
}

The API is tunable using the new server.search stanza, e.g.

server {
  search {
    fuzzy_enabled   = true
    limit_query     = 200
    limit_results   = 1000
    min_term_length = 5
  }
}

These values can be increased or decreased, so as to provide more
search results or to reduce load on the Nomad Server. The fuzzy search
API can be disabled entirely by setting `fuzzy_enabled` to `false`.