Introduce compact keys for JSON metadata fields to reduce size of JSON metadata object

[kuan121]

High Level Changes

1. Introduce compact keys for JSON metadata fields to reduce size of JSON metadata object
2. Remove unnecessary URL scheme, i.e., HTTPS://

Why

This PR is meant to address WietseWind's comment in this discussion about reducing the size of JSON metadata object. With the proposed change, we can achieve a ~27.6% size reduction (from ~626 bytes to ~453 bytes) for the JSON Metadata example provided in XLS-89 Multi-Purpose Token Metadata Schema.

Before

JSON Metadata example (626 bytes)

{
  "ticker": "TBILL",
  "name": "T-Bill Yield Token",
  "desc": "A yield-bearing stablecoin backed by short-term U.S. Treasuries and money market instruments.",
  "icon": "https://example.org/tbill-icon.png",
  "asset_class": "rwa",
  "asset_subclass": "treasury",
  "issuer_name": "Example Yield Co.",
  "urls": [
    {
      "url": "https://exampleyield.co/tbill",
      "type": "website",
      "title": "Product Page"
    },
    {
      "url": "https://exampleyield.co/docs",
      "type": "docs",
      "title": "Yield Token Docs"
    }
  ],
  "additional_info": {
    "interest_rate": "5.00%",
    "interest_type": "variable",
    "yield_source": "U.S. Treasury Bills",
    "maturity_date": "2045-06-30",
    "cusip": "912796RX0"
  }
}

After

JSON Metadata example (453 bytes)

{
  "t": "TBILL",
  "n": "T-Bill Yield Token",
  "d": "A yield-bearing stablecoin backed by short-term U.S. Treasuries and money market instruments.",
  "i": "example.org/tbill-icon.png",
  "ac": "rwa",
  "as": "treasury",
  "in": "Example Yield Co.",
  "us": [
    {
      "u": "exampleyield.co/tbill",
      "c": "website",
      "t": "Product Page"
    },
    {
      "u": "exampleyield.co/docs",
      "c": "docs",
      "t": "Yield Token Docs"
    }
  ],
  "ai": {
    "interest_rate": "5.00%",
    "interest_type": "variable",
    "yield_source": "U.S. Treasury Bills",
    "maturity_date": "2045-06-30",
    "cusip": "912796RX0"
  }
}