Refactor http request code in pkg/quay (konflux-ci#56)

* Refactor http request code in pkg/quay

This refactor helps to reduce duplicate code in pkg/quay and improve the
test coverage in pkg/quay.

Signed-off-by: Chenxiong Qi <[email protected]>

* Add test cases for QuayClient.IsRepositoryPublic

Rewrite the assertions with assert.

Signed-off-by: Chenxiong Qi <[email protected]>

* Use fiction registry API url in tests

Signed-off-by: Chenxiong Qi <[email protected]>

* Do not use underscore in function name

Signed-off-by: Chenxiong Qi <[email protected]>

* Use gock Matcher in pkg/quay test cases

Signed-off-by: Chenxiong Qi <[email protected]>

* Restore quay.io api url in quay_debug_test

I misunderstood the usage of quay_debug_test.go. This patch restores the
API url there and defines a fake url for unit tests specifically.

Signed-off-by: Chenxiong Qi <[email protected]>

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Signed-off-by: Chenxiong Qi <[email protected]>