fix(Configs): Allow hierarchical notation in JSON/YAML configs

[karlmcguire]

(DGRAPH-3078)

If users want the ability to use hierarchical notation in JSON and YAML --config files they can now do so. If not, they can use the SuperFlag string notation as well.

---

JSON:

{
  "mutations": "strict",
  "badger": {
    "compression": "zstd:1",
    "goroutines": 5
  },
  "raft": {
    "idx": 2,
    "learner": true
  },
  "security": {
    "whitelist": "127.0.0.1,0.0.0.0"
  }
}

Is converted into:

{
  "mutations": "strict",
  "badger": "compression=zstd:1; goroutines=5;",
  "raft": "idx=2; learner=true;",
  "security": "whitelist=127.0.0.1,0.0.0.0;"
}

---

YAML:

mutations: strict
badger:
  compression: zstd:1
  goroutines: 5
raft:
  idx: 2
  learner: true
security:
  whitelist: "127.0.0.1,0.0.0.0"

Is converted into:

mutations: strict
badger: "compression=zstd:1; goroutines=5;"
raft: "idx=2; learner=true;"
security: "whitelist=127.0.0.1,0.0.0.0;"

---

This change is