pgAdmin 4 commit: Add experimental scripts for building Debian/Ubuntu p

Add experimental scripts for building Debian/Ubuntu packages.

Code is split into pkg/debian for the Debian/Ubuntu specific parts,
and pkg/linux for generic code that can be used on other distros.

Tested on Debian 10 and Ubuntu 18.04 at present.

Branch
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master

Details
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https://git.postgresql.org/gitweb?p=pgadmin4.git;a=commitdiff;h=a684b48fb399292a64cb96f042870e7f3451d62e

Modified Files
--------------
.gitignore                   |   3 +-
Makefile                     |   8 ++-
pkg/debian/README            |  47 ++++++++++++++
pkg/debian/build.sh          | 108 +++++++++++++++++++++++++++++++
pkg/debian/pgadmin4.conf     |   9 +++
pkg/debian/setup.sh          |  15 +++++
pkg/linux/README             |   3 +
pkg/linux/build-functions.sh | 147 +++++++++++++++++++++++++++++++++++++++++++
pkg/linux/config_distro.py   |   5 ++
pkg/linux/pgadmin4.desktop   |  10 +++
pkg/linux/setup-web.sh       | 109 ++++++++++++++++++++++++++++++++
11 files changed, 462 insertions(+), 2 deletions(-)