feat(cli): expose CLI signer flags as environment variables

[Hacksore]

Expose TAURI_PRIVATE_KEY_PASSWORD, TAURI_PRIVATE_KEY_PASSWORD, and TAURI_PRIVATE_KEY to make it easier to use the CLI in a CI environment.

In theory we can then call this with all the vars set to create a signature.

tauri signer sign *.exe

Although I saw that this renames the vars https://github.com/tauri-apps/tauri/blob/dev/.changes/cli-env-vars.md

I'm assuming that's a v2 breaking change and I'm not sure if I should adopt those values for this PR.

Guidance from the core team is extremely appreciated. thanks!

What kind of change does this PR introduce?

• Bugfix
• Feature
• Docs
• New Binding issue #___
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change?

• Yes, and the changes were approved in issue #___
• No

Checklist

• When resolving issues, they are referenced in the PR's title (e.g fix: remove a typo, closes #___, #___)
• A change file is added if any packages will require a version bump due to this PR per the instructions in the readme.
• I have added a convincing reason for adding this feature, if necessary

Other information

[amrbashir]

Thank you

[amrbashir]

Oh looks like you didn't sign your commits and I can't merge the PR unless they are signed. You need to setup commit signing, then you can sign past commit like this for example.

[Hacksore]

@amrbashir i had to force push so you're commit is partially verified now, not sure if that's a big deal.

[amrbashir]

That should be fine, thanks