Chainlink migration example (#4)

* chainlink example

* fix gitignore

* pr comments

Author: jayantk

price_feeds/evm/chainlink_migration/.gitignore

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+# Compiler files
+cache/
+out/
+
+# Ignores development broadcast logs
+broadcast/
+
+# Docs
+docs/
+
+# Dotenv file
+.env
+
+lib/*
+!lib/README.md
+
+*~
+
+node_modules

price_feeds/evm/chainlink_migration/README.md

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+## Chainlink Migration Example
+
+This example demonstrates how to deploy a Chainlink-compatible application to Pyth Network price feeds.
+The application `src/ChainlinkApp.sol` is designed to use Chainlink price feeds.
+The script `script/PythAggregatorV3Deployment.sol` deploys this application with the [`PythAggregatorV3`](https://github.com/pyth-network/pyth-crosschain/blob/main/target_chains/ethereum/sdk/solidity/PythAggregatorV3.sol) adapter contract, such that it uses Pyth price feeds.
+
+## Installation
+
+This example uses [Foundry](https://book.getfoundry.sh/getting-started/installation), `npm` and `jq`.
+Please install these tools if you don't have them already. 
+
+Install the solidity dependencies by running:
+
+```bash copy
+npm install
+forge install foundry-rs/[email protected] --no-git --no-commit
+```
+
+## Deploy 
+
+To run the deployment script, you will need a blockchain with a Pyth contract, a wallet with some tokens and an RPC node.
+Export the value of your wallet's private key, the RPC URL, and the [Pyth contract address](https://docs.pyth.network/price-feeds/contract-addresses/evm) as environment variables: 
+
+```bash copy
+export PRIVATE_KEY=0x...
+export RPC_URL=https://sepolia.optimism.io/
+export PYTH_ADDRESS=0x0708325268dF9F66270F1401206434524814508b
+```
+
+Then, deploy the contracts by running:
+
+```bash copy
+forge script script/PythAggregatorV3Deployment.s.sol --rpc-url $RPC_URL --broadcast
+```
+
+This command will print something like:
+
+```
+##### optimism-sepolia
+✅  [Success]Hash: 0xbca3b74534042646899091ee6298e42b491e565dc676691291b144d59974fe93
+Contract Address: 0xbac361910F2a8cEB96c9207302acb692B4708a8b
+Block: 10873047
+Paid: 0.001974369167163242 ETH (658123 gas * 3.000000254 gwei)
+
+
+##### optimism-sepolia
+✅  [Success]Hash: 0x45f41d30c1e971d3e2bbc6de4586a5da3633e5051218808a475e75938e78e66b
+Contract Address: 0x481F16240c55631c78fBF5B2B4191Aa98087C355
+Block: 10873047
+Paid: 0.001974369167163242 ETH (658123 gas * 3.000000254 gwei)
+
+
+##### optimism-sepolia
+✅  [Success]Hash: 0xfea9cea348ea62d66305ca46181b4a261afff6ea744a50ba8d6a5766b2fe254f
+Contract Address: 0x1e8ad7B210EA49e2B910C0D74fa259f83f76D64b
+Block: 10873047
+Paid: 0.000676959057315862 ETH (225653 gas * 3.000000254 gwei)
+```
+
+The first two contracts are instances of `PythAggregatorV3` and the final address is the `ChainlinkApp` contract. 
+Set the address of the deployed `ChainlinkApp` contract as an environment variable for later reference:
+
+```
+export CONTRACT_ADDR=0x7E1Bf7047200dB58A0eD8002552e1243B0DB4bfC
+```
+
+## Try it out
+
+The repo provides two scripts for interacting with the deployed application.
+
+First, `script/UpdatePrice.s.sol` updates the on-chain Pyth price.
+Pyth is a pull oracle, so it has permissionless price updates.
+Retrieve a price update and post it on-chain by running the following commands:
+
+```bash
+curl 'https://hermes.pyth.network/v2/updates/price/latest?ids[]=0xff61491a931112ddf1bd8147cd1b641375f79f5825126d665480874634fd0ace&ids[]=0xef0d8b6fda2ceba41da15d4095d1da392a0d2f8ed0c6c7bc0f4cfac8c280b56d' | jq '.binary.data[0]' -r > price_update.txt
+export PRICE_UPDATE="0x`cat price_update.txt`"
+forge script script/UpdatePrice.s.sol --rpc-url $RPC_URL --broadcast
+```
+
+Please see [Schedule Price Updates](https://docs.pyth.network/price-feeds/schedule-price-updates) for ways to schedule on-chain updates to Pyth price feeds.  
+
+Second, `script/GetEthSolPrice.s.sol` interacts with a method on the `ChainlinkApp` contract: 
+
+```bash
+forge script script/GetEthSolPrice.s.sol --rpc-url $RPC_URL --broadcast
+```
+

price_feeds/evm/chainlink_migration/foundry.toml

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+[profile.default]
+src = "src"
+out = "out"
+libs = ["lib"]
+
+# See more config options https://github.com/foundry-rs/foundry/blob/master/crates/config/README.md#all-options