Make ecs platform alb.load_balancer_arn optional

[supaspoida]

Updates the ecs platform plugin to make alb.load_balancer_arn optional as per comment here: #4680 (comment)

Fixes: #4680

[hashicorp-cla]

All committers have signed the CLA.

[paladin-devops]

Hey @supaspoida , thank you for the PR! 😄 Could you also add a changelog to this PR? You can add a release note in a file named 4729.txt to the ./.changelog directory.

[supaspoida]

@paladin-devops took a crack at the changelog, tried to follow patterns from existing entries, let me know if anything is off!

[catsby]

Hey @supaspoida sorry for the delay here; it looks like we need 1 more thing here and that's to run make gen/website-docs and push those changes to this branch. Please let us know if you can run that otherwise we'll need to make a new pr to supersede this one, which we can do and still maintain attribution for you. Thanks!

[supaspoida]

@catsby I had a feeling there was probably a docs update needed, thanks for the pointer!

I've run make gen/website-docs and pushed up a WIP commit here: 509b241

I've left it as a separate WIP commit instead of squashing because I hit issues at the content formatting step here: https://github.com/hashicorp/waypoint/blob/main/Makefile#L209

I got a 404 for the next-hashicorp package. Some googling led me to the @hashicorp/platform-cli package. When I update that line to use @hashicorp/platform-cli I don't get the 404 anymore but I also see a ton of formatting changes in tons (maybe all?) docs files unrelated to the ECS platform ALB config, and the command ends w/a non-zero exit code. I also tried removing that line entirely and was surprised to see the same bulk formatting applied even without it!

All that to say, this is my best attempt at pulling out only the expected docs changes without all of the unrelated formatting updates. If you'd like me to include everything I can do that instead, or if there is something I missing around the mdx formatting let me know!

[paladin-devops]

Hey @supaspoida, thanks again for this PR! We are going to merge this PR in as-is, and open up a quick follow-up for the docs fix. Thank you for your contribution!!