Add a onchain execution on forked network with Hardcoded values.

[Ethnical]

Description

A PR to execute a hard-coded transaction (sent 1wei to 0x4141414142424242414141414242424241414141 with data=0x414243) on forked L1 on Sepolia using a well known privatekey.

From a simple cURL will trigger the onchain execution.

We can see that the transaction on tenderly is a simple movemement of 1 wei to 0x4141414142424242414141414242424241414141 with calldata=0x414243.

Tests

I made some tests using the HTTP API directly using:

curl -X POST http://localhost:8080/api/psp_execution \-H "Content-Type: application/json" \-d '{"pause": true, "timestamp": 1719432011, "operator": "Tom"}'

To make better testing, I had to create a mocking interface:

type SimpleExecutor struct{}

func (e *SimpleExecutor) FetchAndExecute(d *Defender) {
	// Do nothing for now, for mocking purposes
}

To achieve this, I have added a executor to the defender object for helping us in the future for mocking the results.

I haved added multiples unit tests in the file api_test.go for the new created functions.

• TestHTTPServerHasOnlyPSPExecutionRoute(): This ensure the API HTTP is not listenning on another methods or other routes. To make sure no undesired HTTP requests can be crafted on unknown method or path.
• TestDefenderInitialization(): This ensure we can create a defender with a mock FetchAndExecute() method.
• TestCheckAndReturnRPC(): This make sure that the RPC ur is correct and valid RPC. This is particular useful for during the development part to not send transaction accidentally on undesired network.
• TestHandlePostMockFetch(): This test the HTTP status code result to ensure malformed HTTP request return the correct status code.

=== RUN   TestHTTPServerHasOnlyPSPExecutionRoute
--- PASS: TestHTTPServerHasOnlyPSPExecutionRoute (0.00s)
=== RUN   TestDefenderInitialization
--- PASS: TestDefenderInitialization (0.00s)
=== RUN   TestHandlePostMockFetch
=== RUN   TestHandlePostMockFetch/Valid_Request
=== RUN   TestHandlePostMockFetch/Invalid_JSON
=== RUN   TestHandlePostMockFetch/Missing_Fields
=== RUN   TestHandlePostMockFetch/Incorrect_Path_Fields
--- PASS: TestHandlePostMockFetch (0.00s)
    --- PASS: TestHandlePostMockFetch/Valid_Request (0.00s)
    --- PASS: TestHandlePostMockFetch/Invalid_JSON (0.00s)
    --- PASS: TestHandlePostMockFetch/Missing_Fields (0.00s)
    --- PASS: TestHandlePostMockFetch/Incorrect_Path_Fields (0.00s)
=== RUN   TestCheckAndReturnRPC
=== RUN   TestCheckAndReturnRPC/Empty_URL
=== RUN   TestCheckAndReturnRPC/Production_URL
=== RUN   TestCheckAndReturnRPC/Valid_Tenderly_Fork_URL
--- PASS: TestCheckAndReturnRPC (0.00s)
    --- PASS: TestCheckAndReturnRPC/Empty_URL (0.00s)
    --- PASS: TestCheckAndReturnRPC/Production_URL (0.00s)
    --- PASS: TestCheckAndReturnRPC/Valid_Tenderly_Fork_URL (0.00s)
PASS
ok      github.com/ethereum-optimism/monitorism/op-defender/psp_executor        0.924s

Additional context
This is the PR N°3, after this one will make 2 PRs again to complete the psp_executor.
Worth noting there is multiples @todo tags that would be fixed in the future PRs.

I have also improve the current README with the current features.