add .netrc support for git artifacts

# Summary

workflow/artifacts/git/git.go it support private key and passwd, it will be good to support .netrc as well

# Use Cases

When would you use this? normally we store all related passwd into one `.netrc` to access different repo, it will be good to support it directly.

It could work like below

````
- name: git-clone
inputs:
artifacts:
- name: argo-source
path: /src
git:
repo: https://github.com/argoproj/argo-workflows.git
revision: "v2.1.1"
# netrcSecret:
# name: github-creds
# key: netrc
`````

---

**Message from the maintainers**:

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Start in workflow/artifacts/git/git.go and trace how the git artifact currently handles private keys and passwords. Then follow the git artifact input schema and secret wiring to determine how netrcSecret should be represented; done means a configured .netrc can authenticate the example private repository without relying on the existing credential methods.

Written by the indexing model from the issue text.