Always send Bearer auth for OAuth2 connectors

Provider token_type values are not reliably valid HTTP auth schemes
(Slack returns "bot" / "user", some providers send an empty string),
which produces a malformed Authorization header on subsequent
requests. Every OAuth2 connector in this codebase actually uses a
bearer token, so we always send "Bearer".

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

pkg/connector/oauth2.go

@@ -583,6 +583,10 @@ type oauth2Transport struct {
 
 func (t *oauth2Transport) RoundTrip(req *http.Request) (*http.Response, error) {
 	req2 := req.Clone(req.Context())
-	req2.Header.Set("Authorization", t.tokenType+" "+t.token)
+	// tokenType from the provider's OAuth response is not always a valid HTTP
+	// auth scheme (Slack returns "bot" / "user", some providers send an empty
+	// string), so we always send "Bearer" -- the only scheme any connector in
+	// this codebase actually needs.
+	req2.Header.Set("Authorization", "Bearer "+t.token)
 	return t.underlying.RoundTrip(req2)
 }