New option to work with one or more hex.pm mirrors

[pguyot]

This is a successor of #156 (see #194 )

Add a new option called hexpm-mirrors for one or more hex.pm mirrors.
Default list is builds.hex.pm, so behavior is unaffected unless option is
used.

Mirrors will help mitigate recent (and older) issues with official hex.pm mirrors reliability, especially in the context of repositories for which CI performs many queries, some of which may get HTTP errors such as the 502 currently observed.

[paulo-ferraz-oliveira]

I think the default builds.hex.pm should always be the last fallback. @ericmj, thoughts?

In any case, I think it's best the option is named alternative-hexpm-mirrors, as mentioned here.

[pguyot]

I think the default builds.hex.pm should always be the last fallback. @ericmj, thoughts?

In any case, I think it's best the option is named alternative-hexpm-mirrors, as mentioned here.

It does not make much sense to force users to use a default fallback mirror. They should know better if they use the option. hex.pm doesn't do that. Plus it makes testing harder.

[ericmj]

I think the default builds.hex.pm should always be the last fallback. @ericmj, thoughts?

I don't think it has to be the last fallback but we should document that if you override mirrors then it will be removed and have an example that shows how to add it to the end.

[paulo-ferraz-oliveira]

No further implementation -based comments at this moment.

@pguyot, CI is failing. Did you run npm run build-dist and push everything generated locally (that's not .gitignored?)

Edit: nvm, it seems the issue was introduced here, so not related to your changes.

[paulo-ferraz-oliveira]

@ericmj, I'm good to merge. This does not change default behaviour and should be exercised shortly. Do we wanna merge now?

[paulo-ferraz-oliveira]

Released in v1.16.0 / v1.16. Tag v1 moved up...