Automatically add 'apt-transport-https' if any HTTPS mirror being used

["Cirujano Cuesta, Silvano" <silvano.cirujano-cuesta@siemens.com>]

IMHO ISAR should automatically install 'apt-transport-https' during
debootstrapping if any of the provided mirrors uses HTTPS. Let me
elaborate my reasons.

There are two possible scenarios WRT Debian repositories involving
HTTPS:

1. First mirror uses HTTPS
2. First mirror uses HTTP

1. works transparently with debootstrap > 1.0.58 (see [1]), since 'apt-
transport-https' gets automatically added to the packages to install if
the mirror to use (the first one) uses HTTPS.

2. WON'T WORK out of the box, since debootstrap won't install 'apt-
transport-https' automatically (remember that it only uses the first
one and it's not HTTPS). And therefore 'apt-transport-https' isn't
available for installations from other mirrors (some of them being
HTTPS).

Fixing this limitation is not very difficult, but implies overriding
'isar-bootstrap.inc' just to add 'apt-transport-https' to the list of
packages to be installed by debootstrap [2]. That's not convenient, and
kind of overkilling.

Letting ISAR handle it automatically is the solution I'd prefer, since
it's very convenient and elegant and I don't see any drawbacks.

In case I've overseen any drawbacks, then having the possibility of
specifying additional packages to be installed during bootstrapping
with a variable would be much better than overriding 'isar-
bootstrap.inc'.

Any opinions about it?

Regards,
  Silvano

[1]
https://sources.debian.org/src/debootstrap/1.0.110/debian/changelog/?hl
=669#L669

[2]
https://github.com/ilbers/isar/blob/6c5db020b9b837d7b0ce63bfc719f9192e7
25f26/meta/recipes-core/isar-bootstrap/isar-bootstrap.inc#L186