Implement add-buildpack-registry

[elbandito]

Summary (WIP)

This is a new command that allows users to add new buildpack registries to their config.toml file. The user also has the option via --default flag to set the newly added registry as the new default registry.

Output

➜  pack add-buildpack-registry --help                                          
Adds a new buildpack registry to your pack config file

Usage:
  pack add-buildpack-registry <name> <url> <type> (github | git) [flags]

Examples:
pack add-buildpack-registry myregistry github https://github.com/buildpacks/mybuildpack

Flags:
      --default   Set this buildpack registry as the default
  -h, --help      Help for 'add-registry'

Global Flags:
      --no-color     Disable color output
  -q, --quiet        Show less output
      --timestamps   Enable timestamps in output
  -v, --verbose      Show more output

➜ pack add-buildpack-registry buildpack https://github.com/buildpacks/registry github
Successfully added buildpack to buildpack registries

➜ pack add-buildpack-registry buildpack https://github.com/buildpacks/registry github
ERROR: add buildpack registry: Buildpack registry buildpack already exists.  First run remove-buildpack-registry buildpack and try again.

Documentation

• Should this change be documented?
  • Yes, see #___
  • No

Related

Resolves #___

[codecov]

Codecov Report

Merging #847 into main will increase coverage by 0.16%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #847      +/-   ##
==========================================
+ Coverage   76.14%   76.29%   +0.16%     
==========================================
  Files          84       86       +2     
  Lines        4370     4407      +37     
==========================================
+ Hits         3327     3362      +35     
- Misses        699      700       +1     
- Partials      344      345       +1     

Flag	Coverage Δ
#os_linux	76.29% <ø> (+0.16%)	⬆️
#os_macos	72.87% <ø> (+0.19%)	⬆️
#os_windows	100.00% <ø> (ø)
#unit	76.29% <ø> (+0.16%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

[jromero]

Accepted

Some screenshots of the manual tests.