Script should do the following

• Validate the links of the podcasts (whether they are broken)
• Validate the order of the podcasts in each category (and also categories)

Break the build when either of the above validations fail

Please fill in the fields below to submit an issue or feature request. The
more information that is provided, the better.

Description of issue or feature request:

When some metadata is signed with multiple keys, tuf/repository_lib.py doesn't write the signatures in a deterministic order. This occurs because of this [line](https://github.com/theupdateframework/tuf/blob/develop/tuf/r