Replace apt-key with keyring installation (take II)

[j-rivero]

Second take of #74. Reproducing the text here:

As the apt-key man pages recommends, this PR removes the use of it and replaces it with a Signed-By clause that points to a download gpg key.

The PR adds the key_url field to yaml to store the URI to grab the key from. The keyfield is still preserve to check that the key stored has the expected fringerprint to improve the security.

The tool will replace:

• Automatically the files under /etc/apt/config.d/sources.list.d/_gzdev_ files if they exist with a new one using the signed-by clause.
• Previous gzdev installation of gpg keys inside /usr/share/keyring

The tool will not replace:

• Any key authorized before using apt-key or other method.

[j-rivero]

Testing:

[j-rivero]

Another round of tests in