Add ArgochainTestnet configuration (#395)

feat: add Argochain Testnet
(#395)
### Description

<!--
Summary of change.
Example: Add sepolia chain
--> Add Argochain Testnet using the projects' official
docs.

### Backward compatibility

<!--
Are these changes backward compatible? Note that additions are backwards
compatible.

Yes/No
--> No

### Testing

<!--
Have any new metadata configs and deployment addresses been used with
any Hyperlane tooling, such as the CLI?
--> CLI

---------

Authored-by: Pavon Dunbar <pavon@devolvedai.com>

---------

Co-authored-by: Paul Balaji <10051819+paulbalaji@users.noreply.github.com>

.changeset/chilled-wasps-marry.md

@@ -0,0 +1,5 @@
+---
+'@hyperlane-xyz/registry': minor
+---
+
+Adding Argochain Testnet to the Official Hyperlane Github Registry

chains/argochaintestnet/metadata.yaml

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+# yaml-language-server: $schema=../schema.json
+blockExplorers:
+  - apiUrl: https://test-scanner.devolvedai.com/api
+    family: other
+    name: Argochain Testnet Explorer
+    url: https://test-scanner.devolvedai.com
+blocks:
+  confirmations: 1
+  estimateBlockTime: 6
+  reorgPeriod: 20
+chainId: 1298
+deployer:
+  name: pavondunbar
+  url: https://github.com/pavondunbar
+displayName: Argochain Testnet
+domainId: 1298
+isTestnet: true
+name: argochaintestnet
+nativeToken:
+  decimals: 18
+  name: Argocoin
+  symbol: AGC
+protocol: ethereum
+rpcUrls:
+  - http: https://rpc-testnet.devolvedai.com