feat: adding refresh function to useDirectusAuth.ts

[GeoffreyParrier]

Adding support for refresh API without refresh token

Types of changes

• Bug fix (a non-breaking change which fixes an issue)
• New feature (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Description

In case we have an SSO auth, I didn't find and understand how to implement it with nuxt-directus.
I finally chose to help and to add what's missing to use it with SSO Auth.

I didn't fully add /auth/refresh because the refresh token seems unused for now, so I decided to focus on getting the token for SSO Auth.

Resolves: #115

It's my first PR on an open source project, I hope it's a good implement, I can update it in case anything is wrong or missing.

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes (if not applicable, please state why)

[Intevel]

We have to check this, after adding the normal refresh function.