feat: remove empty artifact CLI message and show hints for pulling OCI image layout

[sajayantony]

What this PR does / why we need it:
Update the message for oras pull of an image to something actionable -

The current outputs looks like this

❯ oras pull localhost:5000/hello-world:latest
Downloaded empty artifact
Pulled [registry] localhost:5000/hello-world:latest
Digest: sha256:7e9b6e7ba2842c91cf49f3e214d04a7a496f8214356f41d81a6e6dcad11f11e3

The PR modifies this to

❯ go run ./cmd/oras  pull localhost:5000/hello-world:latest
Skipped pulling layers without "org.opencontainers.image.title"
Use 'oras copy localhost:5000/hello-world:latest --to-oci-layout <layout-dir>' to pull all layers.

Also changed to ✓ character for checkmark.

[sajayantony]

Open to rewording this

Skipped pulling layers without "org.opencontainers.image.title"

Another option would be

Skipped pulling layers without annotation value for "org.opencontainers.image.title"

[qweeah]

LGTM with suggestions:
Action prompt Pulled can be formatted into the same length with Skipped
to make output aligned.

[codecov-commenter]

Codecov Report

Merging #1157 (14833b8) into main (9ec4f1b) will increase coverage by 0.08%.
The diff coverage is 87.50%.

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@@            Coverage Diff             @@
##             main    #1157      +/-   ##
==========================================
+ Coverage   79.85%   79.94%   +0.08%     
==========================================
  Files          65       65              
  Lines        3520     3520              
==========================================
+ Hits         2811     2814       +3     
+ Misses        494      492       -2     
+ Partials      215      214       -1     

Files	Coverage Δ
cmd/oras/internal/display/progress/status.go	95.08% <100.00%> (ø)
cmd/oras/root/pull.go	73.91% <86.66%> (+1.44%)	⬆️