feat: enable importing public-facing ALBs

[huanjani]

Import an existing ALB that is within the deployment environment's VPC by adding

http:
  alb: [name or ARN of ALB]

to a Load-Balanced Web Service's manifest.

Related: #3319, #1457, #3936.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the Apache 2.0 License.

[codecov-commenter]

Codecov Report

Attention: 49 lines in your changes are missing coverage. Please review.

Comparison is base (baf2a78) 69.91% compared to head (413fa79) 69.94%.
Report is 10 commits behind head on mainline.

Additional details and impacted files

@@             Coverage Diff              @@
##           mainline    #5438      +/-   ##
============================================
+ Coverage     69.91%   69.94%   +0.02%     
============================================
  Files           299      301       +2     
  Lines         45497    45901     +404     
  Branches        295      295              
============================================
+ Hits          31810    32105     +295     
- Misses        12141    12232      +91     
- Partials       1546     1564      +18     

Files	Coverage Δ
...ustom-resources/lib/alb-rule-priority-generator.js	98.82% <ø> (ø)
...al/pkg/deploy/cloudformation/stack/transformers.go	88.41% <100.00%> (+0.29%)	⬆️
internal/pkg/describe/lb_web_service.go	65.47% <ø> (ø)
internal/pkg/describe/uri.go	78.71% <100.00%> (+2.28%)	⬆️
internal/pkg/manifest/http.go	76.76% <ø> (ø)
internal/pkg/aws/elbv2/elbv2.go	91.53% <88.00%> (-1.63%)	⬇️
...rnal/pkg/deploy/cloudformation/stack/lb_web_svc.go	83.01% <66.66%> (-0.58%)	⬇️
internal/pkg/template/workload.go	50.59% <29.41%> (-2.33%)	⬇️
internal/pkg/cli/deploy/lbws.go	50.41% <20.51%> (-6.66%)	⬇️

... and 6 files with indirect coverage changes

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[github-actions]

🍕 Here are the new binary sizes!

Name	New size (kiB)	size (kiB)	Delta (%)
macOS (amd)	52348	51976	+0.72
macOS (arm)	53212	52812	+0.76
linux (amd)	46044	45716	+0.72
linux (arm)	45312	45056	+0.57
windows (amd)	43496	43168	+0.76

[Lou1415926]

maybe not in this release, but we might want to consider the http.redirect_to_https manifest field like in

copilot-cli/internal/pkg/template/templates/workloads/partials/cf/https-listener.yml

Line 85 in baf2a78

{{- if $rule.RedirectToHTTPS}}

[iamhopaul123]

The PR mostly looks good to me. Awesome! My main concern is regarding the new imported-alb-resources file (+1 to wx's fb and see comments below)

[iamhopaul123]

[Lou1415926]

feel free to remove the label whenever you are ready!