[docs] explore-ysql: start ysqlsh from correct directory

[bhavin192]

• Changes the directory to /home/yugabyte before starting ysqlsh in the Kubernetes pod, this makes sure the instructions like \i share/*.sql work as expected.
• Ref: [stable/yugabyte] set workingDir to /mnt/disk0 charts#9 (current directory is different if Helm chart is being used.)
• Update remaining kubectl exec commands according to [docs] update kubectl exec commands to use binary names directly #4818

Scenarios Tested

• Tried executing the modified commands to make sure they work as expected.