Support custom endpoints

[kennytm]

Is your feature request related to a problem? Please describe.

tame-gcs currently hardcodes the request URLs

tame-gcs/src/v1/objects/insert.rs

Line 387 in 57dde10

"https://www.googleapis.com/upload/storage/v1/b/{}/o?uploadType=multipart",

tame-gcs/src/v1/objects/get.rs

Line 63 in 57dde10

"https://www.googleapis.com/storage/v1/b/{}/o/{}?alt=json",

If we want to use change the endpoints to use other GCS-compatible services e.g. fake-gcs-server, we will need to manually replace the URLs in the generated http::Request, which is awkward.

Note that the official GCS libraries in all other languages support providing custom endpoints:

• C++
• C#
• Go
• Java
• NodeJS
• Python
• Ruby

Describe the solution you'd like

Have an API specifying which endpoint to use.

Describe alternatives you've considered

Additional context

[Jake-Shadle]

Resolved by #59