Plugin install and uninstall CLI command

# Summary
Provide ArgoCLI command to install the plugins

What change needs making?

# Use Cases

```
argo plugin install /folder path
argo plugin uninstall name
```

When would you use this?

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**Message from the maintainers**:

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The issue names no files or tests; start by locating the ArgoCLI plugin command entry point and reviewing existing plugin commands. Define the install flow for a Git URL and folder path and the uninstall flow by name, then add coverage showing both commands work.

Written by the indexing model from the issue text.