add AltLayer testnet (#2774)

* add AltLayer testnet

* fix altlayer testnet explorer link

* format json and remove slash at end of url for altlayer testnet

_data/chains/eip155-9997.json

@@ -0,0 +1,25 @@
+{
+  "name": "AltLayer Testnet",
+  "chain": "ETH",
+  "rpc": ["https://testnet-rollup-api.altlayer.io"],
+  "faucets": [],
+  "nativeCurrency": {
+    "name": "Ether",
+    "symbol": "ETH",
+    "decimals": 18
+  },
+  "features": [{ "name": "EIP155" }, { "name": "EIP1559" }],
+  "infoURL": "https://altlayer.io",
+  "shortName": "alt-testnet",
+  "chainId": 9997,
+  "networkId": 9997,
+  "icon": "altlayer",
+  "explorers": [
+    {
+      "name": "blockscout",
+      "url": "https://testnet-rollup-explorer.altlayer.io",
+      "icon": "blockscout",
+      "standard": "EIP3091"
+    }
+  ]
+}

_data/icons/altlayer.json

@@ -0,0 +1,8 @@
+[
+  {
+    "url": "ipfs://QmcEfZJU7NMn9ycTAcEooQgGNfa2nYBToSUZHdFCFadcjb",
+    "width": 1080,
+    "height": 1025,
+    "format": "png"
+  }
+]