[Feature request] Make it easier to configure a custom npm registry base URL.

[mk-pmb]

Is your feature request related to a problem? Please describe.
In my network setup, the docker container cannot directly download from https://registry.npmjs.org/ , so I'd like to configure my own npm registry URL pointing to a local mirror.

Describe the solution you'd like
Maybe a docker build arg or something.

Describe alternatives you've considered
Changing the hard-coded URL in fetch-player-dependencies.cr line 86

Additional context

[mk-pmb]

Actually, I have an even better idea. (#4361) I'll leave this around closed to help other people find it who had the same initial approach.

[unixfox]

Feel free to submit a PR for being able to configure the npm registry URL.

There is an example here for using crystal flags:

invidious/src/invidious/routes/misc.cr

Line 1 in 97c4165

{% skip_file if flag?(:api_only) %}