feat: add update to auth cmd

[HatiCode]

Closes #388

📑 Description

This PR adds an update subcommand to the auth command, allowing to update a key in a previously configured provider e.g: password, model...
It also fixes a couple typos met along the way.

✅ Checks

• My pull request adheres to the code style of this project
• My code requires changes to the documentation
• I have updated the documentation as required
• All the tests have passed

ℹ Additional Information

[matthisholleville]

Hello, thank you very much for your contribution. I just reviewed your PR. It seems like it implements an update method that requires setting all the fields. Imagine if the user wants to modify only the password in their configuration or the model without having to fill in all the other fields. I think it would be interesting to lean more towards this implementation.

What do you think ?

[HatiCode]

@matthisholleville indeed this is what I'm trying to achieve, now because I reused the viper.Set() method at line 74, it reimplements all default empty values from the flags declared alongside the changes one. Do you know how I could keep the change passed with a flag and leave the rest untouched ?

[matthisholleville]

Check if the flag is not empty? I don't think flags should have default values in the case of an update.

[HatiCode]

@matthisholleville I made a couple changes and it's now working, changes are only applied for the flags used. I still feel like this could use some nice refactoring at a certain point tho

[matthisholleville]

Hello @HatiCode can you please provide an example of the commande ?

[HatiCode]

@matthisholleville
Let's say I want to update the model I use for openai :
k8sgpt auth update [backend name] [flags] -> k8sgpt auth update openai -m gpt-2