Reset admin password documentation

### Current Behavior

I was not able to find the documentation to reset the admin password.

### Proposed Behavior

Document how to generate a ManagedPassword.

IF you are interested I could integrate the project documentation e.g., inserting the following example python script that does the job

```python
from hashlib import sha512
import bcrypt

password = input("password: ")
prehash = sha512(password.encode()).hexdigest().encode()
salt = bcrypt.gensalt(rounds=14, prefix=b'2a')
phash = brcrypt.hashpw(prehash, salt)
print(phash)
```

### Checklist

- [X] I have read and understand the [contributing guidelines](https://github.com/DependencyTrack/dependency-track/blob/master/CONTRIBUTING.md#filing-issues)
- [X] I have checked the [existing issues](https://github.com/DependencyTrack/dependency-track/issues) for whether this enhancement was already requested