Proposal: Implementation of `purge` command

# Overview

The Harbor CLI implemented numerous commands, integrating most of the Harbor REST APIs, and this proposal adds the `purge` command to that list.

## Proposal

The following is the tentative structure of the `harbor schedule purge` command, So I request the maintainers and community to review this and share suggestions on this.

```md
# Get details of a specific purge job
> harbor schedule purge status

# Stop the purge audit log execution specified by ID
> harbor schedule purge stop

# Get purge job logs
> harbor schedule purge logs

# Get purge jobs' schedule
> harbor schedule purge list

# Get purge jobs results
> harbor schedule purge history

# Create a purge job schedule
> harbor schedule purge create (--cron / -e)

# Update purge's schedule
> harbor schedule purge update (--cron / -e)
```

> cc: @bupd @Vad1mo @OrlinVasilev @NucleoFusion