Add subctl upgrade command

[Jaanki]

Epic Description

A new subctl upgrade command should be added that upgrades the running enviroment to the version specified by the user. The command would do the following:

1. Upgrade subctl itself to the specified version
2. Upgrade Submariner to the specified version by re-running deploy-broker and join.

What it won't do is to change from a non-globalnet environment to globalnet enabled one or vice-versa. Feasibility of adding or removing the Service discovery component needs to be determined.

This is helpful in major and minor version upgrades.

Acceptance Criteria

Submariner environment can be successfully upgraded to the specified version.

Definition of Done (Checklist)

• [ ] Code complete
• [ ] Relevant metrics added
• [ ] The acceptance criteria met
• [ ] Unit/e2e test added & pass
• [ ] CI jobs pass
• [ ] Deployed using cloud-prepare+subctl
• [ ] Deployed using ACM/OCM addon
• [ ] Deploy using Helm
• [ ] Deployed on supported platforms (for e.g kind, OCP on AWS, OCP on GCP)
• [ ] Run subctl verify, diagnose and gather
• [ ] Uninstall
• [ ] Troubleshooting (gather/diagnose) added
• [x] Documentation added
• [x] Release notes added

Work Items

• [ ] Write logic to upgrade subctl
• [ ] Add rerunning deploy-broker command with the specified Submariner version
• [ ] Add rerunning join command with the specified Submariner version

[skitt]

Release notes and documentation: https://github.com/submariner-io/submariner-website/pull/1009