The indent function strips empty lines that might be required

[PascalVA]

Describe the bug

The indent function strips empty lines that might be required. In our example the issue occurs while trying to print a PGP public key block. The empty line is required for the PGP PUBLIC KEY BLOCK to be considered valid.

To Reproduce

1. Create a secret on HashiCorp Vault with the following content

   -----BEGIN PGP PUBLIC KEY BLOCK-----
   
   TmV2ZXIgZ29ubmEgZ2l2ZSB5b3UgdXAKTmV2ZXIgZ29ubmEgbGV0IHlvdSBkb3duCk5ldmVyIGdv
   bm5hIHJ1biBhcm91bmQgYW5kIGRlc2VydCB5b3UKTmV2ZXIgZ29ubmEgbWFrZSB5b3UgY3J5Ck5l
   dmVyIGdvbm5hIHNheSBnb29kYnllCk5ldmVyIGdvbm5hIHRlbGwgYSBsaWUgYW5kIGh1cnQgeW91
   Cg==
   -----END PGP PUBLIC KEY BLOCK-----
   

2. Create a ConfigMap file with the following content and replace the HashiCorp Vault path. (NOTE: the config key here is a multiline-string. Indentation in a yaml structure is not necessary since is already handled corretly by the plugin)

   ---
   apiVersion: v1
   kind: ConfigMap
   data:
     config: |
       pgp_key: |
         <path:/mount_point/data/path/to/secret#key | indent 2>
   

3. Run the argocd-vault-plugin to template the file

   # Version we have deployed
   argocd-vault-plugin_1.17.0_linux_amd64 generate configmap.yaml
   
   # Latest version
   argocd-vault-plugin_1.18.1_linux_amd64 generate configmap.yaml
   

Expected behavior

We expect to have all content returned with proper indentation as below:

apiVersion: v1
data:
  config: |
    pgp_key: |
      -----BEGIN PGP PUBLIC KEY BLOCK-----
      
      TmV2ZXIgZ29ubmEgZ2l2ZSB5b3UgdXAKTmV2ZXIgZ29ubmEgbGV0IHlvdSBkb3duCk5ldmVyIGdv
      bm5hIHJ1biBhcm91bmQgYW5kIGRlc2VydCB5b3UKTmV2ZXIgZ29ubmEgbWFrZSB5b3UgY3J5Ck5l
      dmVyIGdvbm5hIHNheSBnb29kYnllCk5ldmVyIGdvbm5hIHRlbGwgYSBsaWUgYW5kIGh1cnQgeW91
      Cg==
      -----END PGP PUBLIC KEY BLOCK-----
kind: ConfigMap

Screenshots/Verbose output

We receive the output with the empty line removed by the indent plugin.

apiVersion: v1
data:
  config: |
    pgp_key: |
      -----BEGIN PGP PUBLIC KEY BLOCK-----
      TmV2ZXIgZ29ubmEgZ2l2ZSB5b3UgdXAKTmV2ZXIgZ29ubmEgbGV0IHlvdSBkb3duCk5ldmVyIGdv
      bm5hIHJ1biBhcm91bmQgYW5kIGRlc2VydCB5b3UKTmV2ZXIgZ29ubmEgbWFrZSB5b3UgY3J5Ck5l
      dmVyIGdvbm5hIHNheSBnb29kYnllCk5ldmVyIGdvbm5hIHRlbGwgYSBsaWUgYW5kIGh1cnQgeW91
      Cg==
      -----END PGP PUBLIC KEY BLOCK-----
kind: ConfigMap

Additional Infromation

I assume the problem comes from here:

argocd-vault-plugin/pkg/kube/modifiers.go

Lines 49 to 57 in 810f1fe

	if len(lines[i]) > 0 {
	for j := 0; int64(j) < level; j += 1 {
	builder.WriteString(" ")
	}
	builder.WriteString(strings.TrimSpace(lines[i]))
	if i < len(lines)-1 {
	builder.WriteString("\n")
	}
	}

I think the function should always write the trailing newline and not only if the length of the line is greater than 0.