fix: update figma token endpoint (#1952)

## What kind of change does this PR introduce?
* Migrate figma oauth to use endpoint as listed in
https://www.figma.com/developers/api#oauth_migration_guide

Author: kangmingtay

internal/api/external_figma_test.go

@@ -43,7 +43,7 @@ func (ts *ExternalTestSuite) TestSignupExternalFigma() {
 func FigmaTestSignupSetup(ts *ExternalTestSuite, tokenCount *int, userCount *int, code string, email string) *httptest.Server {
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		switch r.URL.Path {
-		case "/api/oauth/token":
+		case "/v1/oauth/token":
 			*tokenCount++
 			ts.Equal(code, r.FormValue("code"))
 			ts.Equal("authorization_code", r.FormValue("grant_type"))

internal/api/provider/figma.go

@@ -51,7 +51,7 @@ func NewFigmaProvider(ext conf.OAuthProviderConfiguration, scopes string) (OAuth
 			ClientSecret: ext.Secret,
 			Endpoint: oauth2.Endpoint{
 				AuthURL:  authHost + "/oauth",
-				TokenURL: authHost + "/api/oauth/token",
+				TokenURL: apiHost + "/v1/oauth/token",
 			},
 			RedirectURL: ext.RedirectURI,
 			Scopes:      oauthScopes,