feat(packaging): add support for ipk package format

[schmidtw]

Adds code to expose the ipk configuration values and registers the ipk package format with nfpm.

Updates the documentation with how to use the new ipk specific configuration parameters.

This isn't ready to merge, but I have some questions

1. I copied the TestIPKSpecificConfig() (code) from the TestAPKSpecificConfig() and found it only is really testing if specific scripts are there or not. Since IPK doesn't have any additional scripts, just fields in one file do I need this test function? Is there a better way to validate the output?
2. I have run into issues where the tests expect goreleaser to be the org & repo - is there a way to override this in my fork without changing the code?
3. Is the ToNFPAlts() and ToNFP() living in the config.go file ok? There wasn't much code in that file, so I figured I'd ask if you'd rather this code be elsewhere.

[schmidtw]

@caarlos0 I'm not sure if GH will ping you on a draft PR so I'm mentioning you here to get some feedback when you get some time. Thank you!

[caarlos0]

this looks good, thank you!

for full transparency: I plan to release v2 as 1.26 minus the deprecations, so this will probably land in v2.1 only.

I'm aiming to release v2 either this weekend or the next, depending if I get any bug reports during this time

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.79%. Comparing base (c68d830) to head (a4320f7).
Report is 281 commits behind head on main.

❗ Current head a4320f7 differs from pull request most recent head 41a5ef6

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4863      +/-   ##
==========================================
+ Coverage   83.77%   83.79%   +0.01%     
==========================================
  Files         135      139       +4     
  Lines       13029    11224    -1805     
==========================================
- Hits        10915     9405    -1510     
+ Misses       1677     1356     -321     
- Partials      437      463      +26     

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[schmidtw]

Do you want me to update the doc to call out v2.1 in the PR & make this a non-draft PR?

[caarlos0]

if you can yeah, I appreciate it! otherwise I can make the changes when the time comes :)