Add mtls cert binding for Cloudflare Workers

[maheshshekhar]

Description

Has your change been tested?

Yes this code has been tested

Screenshots (if appropriate):

Types of changes

What sort of change does your code introduce/modify?

• New feature (non-breaking change which adds functionality)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.
• This change is using publicly documented in cloudflare/api-schemas
  and relies on stable APIs.

[github-actions]

Oops! It looks like no changelog entry is attached to this PR. Please include a release note as described in https://github.com/cloudflare/cloudflare-go/blob/master/docs/changelog-process.md.

Example:

```release-note:TYPE
Release note
```

If you do not require a release note to be included, please add the workflow/skip-changelog-entry label.