[DESIGN]: Improve Adopters contribution flow: Redirect "Submit PR" link to contribution guide

### Describe the Issue

**"Submit a Pull Request" Link leads to raw YAML file without contribution guidelines**

On the **Adopters** page (Case Studies), the "submit a pull request" link directs users specifically to the `website/config/usecases.yaml` file on GitHub.
This lands the user on a raw code view without context, schema definitions, or instructions on how to add their company. This creates friction for new contributors who may not know the required YAML structure or the correct contribution workflow.

### Expected Outcome

The link should direct users to:
1. A **Contribution Guide** explaining how to add a company to the `usecases.yaml` file.
2. OR open the file directly in **GitHub "Edit" mode** to save a click.
3. OR a GitHub Issue Template for adding a new adopter.

**Actual Behavior**
The link opens the read-only file view (`blob`) of `usecases.yaml`. The user has to figure out the schema and manually click "Edit" to proceed.

### Screenshots

### Steps to Reproduce

1. Navigate to `https://asyncapi.com/casestudies`.
2. Scroll down to the **Adopters** section.
3. Click the link labeled **"submit a pull request"**.
4. Observe that it opens the GitHub file view for `usecases.yaml`.

### Browser/Device

**URL:** https://asyncapi.com/casestudies
**Target Link:** [Submit a pull request](https://github.com/asyncapi/website/blob/master/config/usecases.yaml)
**Browser:** Chrome
**Operating System:** Windows 11

### Additional Notes

_No response_

### Check Before Submitting

- [x] I have looked for similar issues to avoid duplicates.
- [x] I have reviewed the [Contributing Guidelines](https://github.com/asyncapi/.github/blob/master/CONTRIBUTING.md).

### Would you like to help fix this issue? (Not required, but appreciated!)

- [x] Yes, I am interested in contributing to the fix.
- [ ] No, I am just reporting the issue.

Start at the Adopters section on https://asyncapi.com/casestudies and trace its current "submit a pull request" link to the page implementation; the target data file is website/config/usecases.yaml. Reproduce the raw-file navigation, then confirm which proposed destination maintainers want and verify the link opens that contribution guide, edit view, or issue template.

Written by the indexing model from the issue text.