Add a couple of Kubernetes questions and exercises

Also updated CKA page.

topics/kubernetes/exercises/labels_and_selectors/exercise.md

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+# Labels and Selectors 101
+
+## Objectives
+
+1. How to list all the Pods with the label "app=web"?
+2. How to list all objects labeled as "env=staging"?
+3. How to list all deployments from "env=prod" and "type=web"?
+
+## Solution
+
+Click [here](solution.md) to view the solution.

topics/kubernetes/exercises/labels_and_selectors/solution.md

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+# Labels and Selectors 101
+
+## Objectives
+
+1. How to list all the Pods with the label "app=web"?
+2. How to list all objects labeled as "env=staging"?
+3. How to list all deployments from "env=prod" and "type=web"?
+
+## Solution
+
+`k get po -l app=web`
+`k get all -l env=staging`
+`k get deploy -l env=prod,type=web`

topics/kubernetes/exercises/taints_101/exercise.md

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+# Taints 101
+
+## Objectives
+
+1. Check if one of the nodes in the cluster has taints (doesn't matter which node)
+2. Create a taint on one of the nodes in your cluster with key of "app" and value of "web" and effect of "NoSchedule"
+   1. Explain what it does exactly
+   2. Verify it was applied
+
+## Solution
+
+Click [here](solution.md) to view the solution.
+
+1. `kubectl describe no minikube | grep -i taints`
+2. `kubectl taint node minikube app=web:NoSchedule`
+   1. Any resource with "app=web" key value will not be scheduled on node `minikube`
+   2. `kubectl describe no minikube | grep -i taints`