Feature/526 add basic auth

Describe the MR

Adds login screen, logout button, and session management in panto-web:

• Login screen

• Logout button

• Login format error

• Credentials error

Why was this MR needed?

Now that panto requires authenticated request (see !461 (merged)), panto-web needs to successfully go through the authentication process to get a token (see #526 (closed) for implementation details and scenarios)

Extra-care points?

Does this MR meet the acceptance criteria?

• Documentation created/updated
• CHANGELOG updated
• Unit Tests added/updated

What are the relevant issue numbers?

Closes #526 (closed)

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