feat: add node to a cluster

[dkeven]

• Background

Currently, a local and single node environment is assumed in the Olares installer, this PR adds a joincluster.sh that can be executed on a new machine to let it join an already existing Olares cluster.

What the new script does, effectively, is read a bunch of environment variables that specify how to access the master node through SSH, run the corresponding commands of olares-cli to retrieve the Olares version of the master node, download and install the container components and join the cluster.

Specifically, the environment variables read by the new joincluster.sh script are:

name	explain	required	default
MASTER_HOST	the IP address of the master node	true
MASTER_NODE_NAME	the node name of master	false
MASTER_SSH_USER	the Linux user name to login to the master node by SSH	false	root
MASTER_SSH_PASSWORD	the password of the Linux user	true for non-root master-ssh-user
MASTER_SSH_PRIVATE_KEY_PATH	the private SSH key to authenticate as the Linux user	false	/root/.ssh/id_rsa
MASTER_SSH_PORT	the listening port of the SSH service on the master node	false	22

• Target Version for Merge
  v1.12.0

• Related Issues
  none

• PRs Involving Sub-Systems
  feat: add worker node to the cluster Installer#93

• Other information:
  none