chore: create generic clickup/Client.get method

[prgres]

Summary

A lot of time has flown by since I was doing anything inside the clickup pkg but today I saw there is a lot of code duplication that can be simplified.

• added func (c *Client) get(url string, objmap RequestGet) error and accepts
  • url string for c.requestGet(url) to fetch data from Clickup API
  • objmap RequestGet as an interface to which that data is loaded
• added type RequestGet interface that only requires Error() string) method. Any RequestGet* struct must implement it
• added ViewType type
• now pkg returns all views without any filtering. It is now api pkg's responsibility. It improves decoupling