Drop unused OktaProvider const, wrap parse error

OktaProvider was dead: the provider-string const is only matched by
OAuth providers (SlackProvider in oauth2.go / connector.go), and an
API-key connector never matches on it.

Wrap the url.Parse error in nextPageURL with %w, like every sibling
driver, instead of dropping it.

Signed-off-by: Aurélien Sibiril <81782+aureliensibiril@users.noreply.github.com>

pkg/accessreview/drivers/okta.go

@@ -175,7 +175,7 @@ func (d *OktaDriver) nextPageURL(linkHeader string) (string, error) {
 
 	u, err := url.Parse(raw)
 	if err != nil {
-		return "", fmt.Errorf("cannot parse okta next-page link")
+		return "", fmt.Errorf("cannot parse okta next-page link: %w", err)
 	}
 
 	// Pin the next page to the same https origin: reject a scheme downgrade