Refactor image pulling to use goroutines for concurrency

[corang]

Description

Concurrently retrieves image metadata and layers during package create.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Other (security config, docs update, etc)

Checklist before merging

• Test, docs, adr added or updated as needed
• Contributor Guide Steps followed

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[corang]

bigbang example package generation
goroutine branch run times:

real    2m35.223s
user    6m15.280s
sys     0m59.717s
---
real    2m36.357s
user    6m20.161s
sys     0m59.530s
---
real    2m35.577s
user    6m24.044s
sys     0m56.640s

0.28.0 run times:

real    3m35.299s
user    9m21.381s
sys     0m47.760s
---
real    3m34.414s
user    9m33.166s
sys     0m46.836s
---
real    3m41.898s
user    8m47.642s
sys     0m44.218s

0.28.0 skip sbom run times:

real    2m28.487s
user    2m38.983s
sys     0m12.519s
---
real    2m22.387s
user    2m37.232s
sys     0m13.272s
---
real    2m22.329s
user    2m36.669s
sys     0m12.810s

[corang]

tldr:

• goroutine avg 2m35.719s
• v28 normal avg 3m37.204s
• v28 skip avg 2m24.401s

sbom creation time is now 11s vs 1m13s on my machine with the bigbang example package

[corang]

hijacked the PR to include image pull concurrency too @Racer159 Can move it to another PR if it's not wanted here.

[corang]

Creating the BB package on my machine with cached images is now 0m56.267s vs 3m37.204s on v0.28.0

[corang]

Don't know why ci is failing, same commands work fine on my local machine