Configure default timeout for all API calls

**What is the feature and why do you need it**:
All API calls done through this client today goes through urllib3, where the timeout is default to set to None, this means infinite timeout and is a well known pitfall with urllib3. Lost connection attempts can get stuck waiting forever, with no retries being done to reestablish the connection.

[Quoting the requests-documentation](https://requests.readthedocs.io/en/latest/user/quickstart/#timeouts) which uses urllib3 under the hood:

> _Nearly all production code should use this parameter in nearly all requests. Failure to do so can cause your program to hang indefinitely:_

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There is a `_request_timeout` kwargs argument that can be set on each api-call, but that is both tedious, easy to forget and not type-checked due to use of kwargs-dictionarly.

**Describe the solution you'd like to see**:
Similar to how `retries` is configured, `Configuration` should accept a timeout-argument, this can be forwarded into urllib3s poolmanager where it uses this timeout for all operations where an explicit timeout is not provided.