Remove fmt and vet checks from CI (#13063)

* Remove fmt and vet checks from CI

- golangci-lint already does the vet and fmt checks. Remove those
as it is redundant now.
- Also start running golangci-lint as part of the CI pipeline now
just as an extra layer of reliability.

* Incorporate review comments

* Adding golangci install to Jenkinsfile.pr too

* dummy commit to test jenkins

* Trying after cd to directory

* Fix ineffective assign

model/config_test.go

@@ -170,7 +170,6 @@ func TestConfigIsValidFakeAlgorithm(t *testing.T) {
 	require.Equal(t, "model.config.is_valid.saml_canonical_algorithm.app_error", err.Message)
 	*c1.SamlSettings.CanonicalAlgorithm = temp
 
-	temp = *c1.SamlSettings.SignatureAlgorithm
 	*c1.SamlSettings.SignatureAlgorithm = "Fake Algorithm"
 	err = c1.SamlSettings.isValid()
 	if err == nil {