support target and empty output

[hirosassa]

In this PR, I implemented followings:

• target variable support which adds target variable on comment title.
• no changes output which display no changes explicitly.

If you run ksnotify --target sample then we get following output:

---

Plan result (sample)

CI link

• updated
  • apps.v1.Deployment.test.test-app

Details (Click me)

apps.v1.Deployment.jasmine.test-app

 @@ -5,7 +5,6 @@
     deployment.kubernetes.io/revision: "3"
+  labels:
+    app: test-app
   name: test-app
   namespace: test
 spec:
@@ -27,7 +26,6 @@
       creationTimestamp: null
       labels:
         app: test-app
-        skaffold.dev/run-id: 1234
     spec:
       containers:
       - args:

---

If you run ksnotify without any change in k8s configuration then we get following output:

---

Plan result (sample)

CI link

No changes. Kubernetes configurations are up-to-date.

[codecov-commenter]

Codecov Report

Merging #30 (4e974ac) into main (b8c5e5b) will increase coverage by 4.78%.
The diff coverage is 79.09%.

@@            Coverage Diff             @@
##             main      #30      +/-   ##
==========================================
+ Coverage   65.00%   69.78%   +4.78%     
==========================================
  Files           7        7              
  Lines         500      599      +99     
==========================================
+ Hits          325      418      +93     
- Misses        175      181       +6     

Impacted Files	Coverage Δ
src/ci.rs	0.00% <0.00%> (ø)
src/main.rs	1.96% <0.00%> (-0.48%)	⬇️
src/template.rs	94.40% <96.66%> (+21.99%)	⬆️

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