gpg.export_key add output and bare functionality

[leifliddy]

What does this PR do?

It adds output and bare functionality to the export_key gpg function

What issues does this PR fix or reference?

Fixes: #62978

Merge requirements satisfied?

[NOTICE] Bug fixes or features added to Salt require tests.

• Docs
• Changelog - https://docs.saltproject.io/en/master/topics/development/changelog.html
• Tests written/updated

Commits signed with GPG?

Yes

[leifliddy]

Note:

1. A passphrase is not needed to export a public key -- it's only needed to export an encrypted private (aka secret) key.
   The logic in gpg module and tests has been updated to reflect that.
2. The gpg function export_keys only returns string data and not a result object. Since we can't query result.status, we must infer whether export_keys was successful of not by simply checking to see whether it returned anything. It's pretty basic, but it's better then nothing. It's the same thing you'll encounter when exporting a key with gpg on the cmd line. Because of this, I thought it was best to keep the tests the same and have them all use bare=True so they can continue to inspect the returned data (vs checking to whether res is True)
3. The benefit this PR provides is the ability to export keys to disk vs simply displaying them on the screen.
4. This PR was recently merged: Add ability to export key(s) to a file.  vsajip/python-gnupg#212
   This will allow the gpg export_keys function to write key data directly to disk.
   We can use this functionality at some point in the future so we could avoid having to write the key data to disk ourselves.

with salt.utils.files.flopen(output, "w") as fout:
    fout.write(salt.utils.stringutils.to_str(result))

[leifliddy]

Update:
I need to rebase my changes to this PR as I submitted multiple gpg.py PRs at once.
I'd like to wait until this PR gets approved #62977 before doing that so I don't have to rebase this PR multiple times.

[Ch3LL]

is this ready for review?

[leifliddy]

Yes, could you please review it and let me know what you think?

[leifliddy]

@Ch3LL Ok I just pushed the requested changes except for the file write one. Could you please review my comment on that when you can?