ci(benchmarks): run nightly benchmark and create PR (#2915)

## Linked Issues/PRs
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closes https://github.com/FuelLabs/fuel-core/pull/2915

## Description
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This pull request introduces a new GitHub workflow to automate the
nightly gas costs benchmark process. The workflow schedules a nightly
benchmark run, processes the results, and optionally creates a pull
request with the updated benchmark data.

Key changes include:

* **New Workflow Addition:**
* Added a new GitHub Actions workflow named `Nightly Gas Costs
Benchmark` to `.github/workflows/nightly-benchmark.yml`. This workflow
is scheduled to run nightly and can be manually triggered.

* **Environment Variables:**
* Defined environment variables such as `GIT_REPO`, `GIT_REPO_NAME`,
`CARGO_TERM_COLOR`, `RUST_VERSION`, and `CONSENSUS_PARAMETERS_VERSION`
for use within the workflow.

* **Benchmark Job:**
* Created a `benchmark` job that runs on the `fuelcore-benchmark`
runner, checks out the repository, installs the Rust toolchain, caches
dependencies, and runs the benchmarks. The results are processed and
stored in `nightly_benchmarks.json`.

* **Pull Request Creation:**
* Added a `create_pr` job that depends on the `benchmark` job. If
triggered, it updates the `chain_config.json` file with the new
benchmark results, commits the changes, and creates a pull request.