Add --ttl cli option #9

Overview

For ease of use, add a --ttl option, which overrides whatever is set in --config.

Requirements

• --ttl option added to cli
• if set --ttl is used for the evidences ttl

So an execution setting a ttl of 30 days would be: plant push-remote https://github.com/org-foo/repo-bar --ttl 2592000 my_markdown_file.md

Approach

Provide a detailed approach to satisfy all of the requirements listed in the
previous section. This level of detail may not be available at the time of
issue creation and can be completed at a later time.

Security and Privacy

Provide the impact on security and privacy as it relates to the completion of
this issue. This level of detail may not be available at the time of
issue creation and can be completed at a later time. N/A if not applicable.

Test Plan

Provide the test process that will be followed to adequately verify that the
approach above satisfies the requirements provided. This level of detail may
not be available at the time of issue creation and can be completed at a later
time.