[Enhancement] - Allow multiple filters per request

[ribtoks]

Describe the bug
I cannot receive a list of instances filtered with tag and region using ListInstances API, because I'm receiving an error "Only one filter per request is allowed.". This error is frustrating to me because:

• to achieve what I want, now I would need to create artificial tags that will consist of my old tags + concatenated region field (which is a "workaround engineering" that will require additional maintenance effort)
• I do not understand such restriction necessity

To Reproduce
Steps to reproduce the behavior:
Construct govultr.ListOptions specifying Tag and Region in a single object.

Expected behavior
A ListInstances API call succeeds and returns instances in the specified region with the specified tag.

Screenshots

Desktop (please complete the following information where applicable:

• OS: -
• Language Version Go 1.17
• Browser -
• Version -

Additional context

[ddymko]

@ribtoks We'll look into this for you

[ddymko]

@ribtoks This error looks like it is coming back from API. We'll have to take a look at the API. I'll make an internal ticket to dig into this on the API side and get back to you.

[ribtoks]

@ddymko Thank you very much!