Import Erlang advisory in GitHub importer

Since the [elixir_security.py](https://github.com/nexB/vulnerablecode/blob/40a39743f385bd5b6dfa3424bc72231fe1ae7456/vulnerabilities/importers/elixir_security.py) relies on https://github.com/dependabot/elixir-security-advisories, which has been archived by GitHub, we will not be able to access the most recent HEX advisories.

Solution:
- [ ] https://github.com/nexB/vulnerablecode/pull/1061 **keep it, but as a one-time importer**
- [ ] Import Erlang advisory in GitHub importer `(preferred)`
OR
- [ ] Import Hex advisory from OSV

`Erlang ecosystem => package written either in Erlang, Elixir, LFE or Joxa => Hex is the package manager for Erlang ecosystem`

Edit: [mirego/elixir-security-advisories](https://github.com/mirego/elixir-security-advisories) is the actively maintained fork of elixir-security-advisories