Simplify Zendesk driver and share time parsing

Drop the zendeskRole helper and use the raw API role, matching the other
drivers. Factor the duplicated RFC3339 timestamp parsing (parseZendeskTime
and parseDatadogTime were identical) into a shared parseRFC3339Ptr in
driver.go.

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

pkg/accessreview/drivers/zendesk_test.go

@@ -44,7 +44,7 @@ func TestZendeskDriver(t *testing.T) {
 	require.NotNil(t, r.Active)
 	assert.True(t, *r.Active)
 	assert.True(t, r.IsAdmin)
-	assert.Equal(t, "Admin", r.Role)
+	assert.Equal(t, "admin", r.Role)
 	assert.Equal(t, coredata.AccessEntryAccountTypeUser, r.AccountType)
 	assert.Equal(t, coredata.MFAStatusEnabled, r.MFAStatus)
 	assert.Equal(t, coredata.AccessEntryAuthMethodUnknown, r.AuthMethod)
@@ -59,7 +59,7 @@ func TestZendeskDriver(t *testing.T) {
 	require.NotNil(t, r2.Active)
 	assert.True(t, *r2.Active)
 	assert.False(t, r2.IsAdmin)
-	assert.Equal(t, "Agent", r2.Role)
+	assert.Equal(t, "agent", r2.Role)
 	assert.Equal(t, coredata.MFAStatusDisabled, r2.MFAStatus)
 	assert.Nil(t, r2.LastLogin)
 }