add support for optarch to GoPackage easyblock

[lexming]

No description provided.

[lexming]

Tests on x86_64:

• Default: no optarch results in v3
  https://gist.github.com/lexming/77df188bf1595af79cf787a46a19dd75
• Generic: optarch=GENERIC results in v1
  https://gist.github.com/lexming/f830c4ca3c6f35aa44aa3f7fcdb8bb91
• Custom: optarch=AVX512 results in v4
  https://gist.github.com/lexming/aeb0f0a2ab19dfd3bf1d51e74dd25ff9
• Custom: optarch=x86-64-v2 results in v2
  https://gist.github.com/lexming/616152be2b03cc89d645bbce97207c83
• Non-existent: optarch=nonexistent results in warning and Go auto-detect
  https://gist.github.com/lexming/7f427e79d6077c9f46c2f86581668ede

[boegel]

@lexming I changed to target branch in this PR from 5.0.x to develop, you should synchronize your PR branch with current develop branch (which has received a massive update after the release of EasyBuild v5.0.0, see #3670)

[smoors]

lgtm