Bitbucket Cloud - Support Bearer authentication with API Token for

### 📜 Issue Labels

- [x] Please familiarize yourself with the issue labels used in this project: [LABELS.md](https://github.com/backstage/backstage/blob/master/LABELS.md)

### 🔎 Search Terms

```plain
bitbucket
```

### 🗃️ Project Area

Core Framework

### 🔗 External Integration

Bitbucket Cloud

### 📝 Description & Context

Per Bitbucket documentation, there is one additional authentication mechanism when comes to API tokens. see https://support.atlassian.com/bitbucket-cloud/docs/using-api-tokens/ - section titled "Using Bearer authentication". This is currently not supported by the `BitbucketCloudClient`. It only supporst OAuth and Basic authentication with username and password.

### 👍 Expected Behavior

I expect to support "bearer" authentication with API token

### 📦 Reproduction Repo

_No response_

### 🥾 Reproduction steps

1. Configure Bitbucket cloud integration with a api token like this
```yaml
integrations:
bitbucketCloud:
- token: my-token
```
2. Observe all bitbucket calls using anonymous access, instead of authentication with a bearer token.

### Have you read the Code of Conduct?

- [x] I have read the [Code of Conduct](https://github.com/backstage/backstage/blob/master/CODE_OF_CONDUCT.md)

### Are you willing to submit PR?

Yes, and I have enough information to get started