archlinux importer: package url is wrong according to purl-spec

[sify21]

Currently purl from archlinux importer is formatted as pkg:pacman/archlinux/{name}@{version}

But according to the official docs: https://github.com/package-url/purl-spec/blob/master/PURL-TYPES.rst

alpm should be used as type field instead of pacman. (Actually there is no pacman type).
arch, arch32, archarm, manjaro or msys should be used as namespace field instead of archlinux.

alpm

alpm for Arch Linux and other users of the libalpm/pacman package manager.

• There is no default package repository: this should be implied either from
  the distro qualifiers key or using a repository base url as
  repository_url qualifiers key.

• The namespace is the vendor such as arch, arch32, archarm,
  manjaro or msys. It is not case sensitive and must be lowercased.

• The name is the package name. It is not case sensitive and must be lowercased.

• The version is the version of the package as specified in vercmp(8) as part of alpm.

• The arch is the qualifiers key for a package architecture.

• Examples::

  pkg:alpm/arch/pacman@6.0.1-1?arch=x86_64
  pkg:alpm/arch/python-pip@21.0-1?arch=any
  pkg:alpm/arch/containers-common@1:0.47.4-4?arch=x86_64
  

[TG1999]

@sify21 thanks for pointing this, this is under progress in #935

[TG1999]

@sify21 thanks for raising this, this is now fixed. I am closing this now.