test(explorer): set a max_batch_size to the explorer

[avilagaston9]

Motivation

This PR is solely to test #1198

Description

How to Test

1. Start anvil:

make anvil_start_with_block_time

2. Start the explorer

make explorer_build_db
make explorer_create_env
make run_explorer

3. Start the test:

cd operator/pkg
go test -run TestGetBatchExplorerOOM -v -timeout 0

In the explorer, you should be able to see the following output:

[error] Error calculating proof hashes: {:http, :body_too_large}