Issue:
[REFACTOR] Unify the `sandbox` and `production` cargo features

### Description

After #1349, this is the next step towards using a single Docker image across all our environments (see #1346). The `sandbox` and `production` features would have to be unified into a single `release` feature instead. This change would also need corresponding changes in the `Dockerfile` and CI workflows.

Resolution:
<think>
PR Context:
- Title: build: unify `sandbox` and `production` cargo features as `release`
- Merged: 2023-06-07T08:34:58Z
- Files changed: 4 files
- Commits: 3 commits

Implementation approach:
## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [ ] Bugfix
- [ ] New feature
- [ ] Enhancement
- [x] Refactoring
- [ ] Dependency updates
- [ ] Documentation
- [ ] CI/CD

## Description
<!-- Describe your changes in detail -->
This PR unifies the `sandbox` and `production` cargo features into a single feature named `release`.

## Motivation and Context
<!--
Why is this change required? What problem does it solve?
If it fixes an open issue, please link to the is
</think>

To implement this, you'll need to modify:


**Detailed Implementation:**


**Commit 1:** build: unify `sandbox` and `production` cargo features as `release` (#1356)
Files to modify:


**crates/router/src/core/payment_methods/transformers.rs**
  Modify existing code