Update variable get to retrieve multiple variables

The variable get command should support getting multiple variables.

Updated the variable command to support multiple variables. Updated go.mod to pull in the latest api that includes the latest hostfactory ID parser.

Getting a single variable will print out the variable as before

root@addd497790bd:/home/rob/cyberark/conjur-cli-go#  conjur variable get -i secret
George

Getting multiple secrets will print out the secret and the full variable name

root@0d7803c6039d:/home/rob/cyberark/conjur-cli-go# conjur variable get -i secret,top-secret
{
    "secret": "George"
    "top-secret": "Astro"
}

Note: The Python CLI requires the two variables to be separated by a space, and the conjur CLI requires a comma

CyberArk internal issue ID: ONYX-33517

At least 1 todo must be completed in the sections below for the PR to be merged.

[x] The CHANGELOG has been updated, or
[ ] This PR does not include user-facing changes and doesn't require a CHANGELOG update

[x] This PR includes new unit and integration tests to go with the code changes, or
[ ] The changes in this PR do not require tests

[ ] Docs (e.g. READMEs) were updated in this PR
[ ] A follow-up issue to update official docs has been filed here: [insert issue ID]
[x] This PR does not require updating any documentation

[x] This PR changes product behavior and has been reviewed by a PO, or
[ ] These changes are part of a larger initiative that will be reviewed later, or
[ ] No behavior was changed with this PR

[ ] Security architect has reviewed the changes in this PR,
[ ] These changes are part of a larger initiative with a separate security review, or
[x] There are no security aspects to these changes

cyberark / conjur-cli-go