Support netrc-based credentials in buf-setup-action

[tonyli233]

Added two optional input "buf_user" and "buf_token".
If both inputs are supplied, perform logging into Buf registry with the supplied credentials.

[elliotmjackson]

Also make changes to the readme here to supply new config items

[doriable]

Instead of a nested if... else if block, we could probably use early returns to handle the log statements for readability:

if (bufUser !== "" && bufToken !== "" {
    // the logic you already have, which is great
    return null;
}
if (bufUser !== "") {
    core.info(`buf_user is supplied, must also supply...`)
    return null;
}
if (bufToken !== "") {
    // same logic
    return null;
}
core.info(`buf_user and buf_token are not configured, not logging into Buf Schema Registry`)
return null;

[tonyli233]

Thank you for bringing this up! I have updated this in a recent commit.

[doriable]

I don't know why it submitted as approve, I mean to comment! Sorry!

[CLAassistant]

All committers have signed the CLA.

[tonyli233]

I have made the changes requested and update the readme.

[elliotmjackson]

i believe this should live under "Other Configurations" just like "Buf token" does

[elliotmjackson]

Suggested change

	#### Buf username and Buf API token
	Optionally, you can supply both `buf_user` and `buf_api_token` input so that it will perform
	[Buf Schema Registry][bsr] (BSR) authentication at the same time. This will allow you to access
	the private remote packages in BSR. This only works when both `buf_user` and `buf_api_token` are
	supplied at the same time:
	```yaml
	steps:
	- uses: bufbuild/buf-setup-action@v1.11.0
	with:
	buf_user: ${{ secrets.buf_user }}
	buf_api_token: ${{ secrets.buf_api_token }}
	```
	#### Buf username and Buf API token
	If you are using Private [Remote Packages](https://docs.buf.build/bsr/remote-packages/overview) you may need to authenticate the entire system to successfully communicate with the [Buf Schema Registry][bsr]. To achieve this, supply both `buf_user` and `buf_api_token`. This will add your auth credentials to the `.netrc` and allow you to access the BSR from anything in your `PATH`.
	```yaml
	steps:
	- uses: bufbuild/buf-setup-action@v1.11.0
	with:
	buf_user: ${{ secrets.buf_user }}
	buf_api_token: ${{ secrets.buf_api_token }}

[tonyli233]

I think place it in the "Parameters" section better describes its usage. So I think this can stay here to avoid confusion with "Buf token"

[elliotmjackson]

so the two methods to auth with buf are separated? buf_token is also a parameter. what does that mean for your reasoning?

[tonyli233]

buf_token is a env var instead of an input to buf-setup-action. That's why I want to separate them by "Input" and "Other Configuration". I just changed the section name from "parameter" to "input".

[doriable]

Stamping for the code changes and to unblock :)