Add SMTP login to rtems-tools mailer

[Alex White]

The ability to provide a username and password to perform an SMTP login should be added so that rtems-test results can be mailed via an external SMTP server that requires authentication.

The following additional command line options should be enough to make it work:
--smtp-port
--smtp-user
--smtp-password

The mail-related command line options should be filtered from the mailed logs so that credentials do not get leaked.

[Alex White]

Replying to Alex White:

The following additional command line options should be enough to make it work:
--smtp-port
--smtp-user
--smtp-password

Additionally, a --smtp-use-gitconfig option to use the information found in ~/.gitconfig would be nice.

[Alex White <alex.white@…>]

In 1a575af/rtems-tools:

rtemstoolkit/mailer.py: Return full smtp-host arg value

This fixes mail.smtp_host() so that it returns the full argument value
rather than just the second character.

Updates #4384

[Alex White <alex.white@…>]

In 92f7f67/rtems-tools:

rtemstoolkit: Filter mail options from log output

This filters mail-related options out before logging the command line
options. This is needed to prevent leaking potentially sensitive
information via logs and emails.

Updates #4384

[Alex White <alex.white@…>]

In 3b1407f/rtems-tools:

rtemstoolkit/mailer.py: Add SMTP login options

This adds more options so that the user can authenticate with the SMTP
server.

Updates #4384

[Alex White <alex.white@…>]

In 82b752a/rtems-tools:

rtemstoolkit/mailer.py: Add --use-gitconfig option

This adds the option to pull mail-related configuration values from the
user's git configuration.

Closes #4384