Support extra user agent

[ajzkk]

Support extra user agent

result := &omise.Account{}

// pass extra user agent
client.WithUserAgent("OmiseShopify/2.0.0 CheckoutPage/1.0.0") 

err := client.Do(result, &operations.RetrieveAccount{})

Above code will become user agent as OmiseShopify/2.0.0 CheckoutPage/1.0.0 OmiseGo/1.0.12 Go/go1.21

[nuxzero]

Will this impact to Superset's analytics?

[aashishgurung]

I was thinking we could use WithCustomHeaders for this but with this in place, we might not need it. Do we find any use case for WithCustomHeaders? If not then let's remove it.

Or maybe not since there might be people using it although I highly doubt it.