Add S3 action support with labels and improve action display

[fjerlov-cs]

Add S3 action support, labels for all actions, and clean up dead code

• Add S3Action type with GraphQL mutations, API client support, and
  version-gated backward compatibility (requires LogScale >= 1.221.0)
• Add ListActionsWithoutS3 GraphQL query as a fallback for older servers
• Add labels field to all action types and display in list/show commands
• Define ActionType constants to replace duplicated string literals
• Remove unused getActionLabels function, Labeled interface, and legacy
  parser APIs
• Remove legacy parser version-gating and associated GraphQL operations
  (LegacyDeleteParserByID, LegacyCreateParser, LegacyGetParser) along
  with the LogScaleVersionWithParserAPIv2 constant
• Remove deprecated isStarred field from alerts
• Set Type field on all Add() return values for consistency

[fjerlov-cs]

Running on 1.219.1

➜  cli git:(feature/s3-action) ✗ go run github.com/humio/cli/cmd/humioctl actions install fjerlov-test --file ./MyS3Action.yaml
Error installing action: S3 actions require LogScale version 1.221.0 or later
exit status 1
➜  cli git:(feature/s3-action) ✗ go run github.com/humio/cli/cmd/humioctl actions list fjerlov-test                     
       NAME      |     TYPE      |    LABELS      
+----------------+---------------+---------------+
  webhook-action | WebhookAction | test-1,test-2  
➜  cli git:(feature/s3-action) ✗ go run github.com/humio/cli/cmd/humioctl actions show fjerlov-test MyS3Action
Error fetching action: action "MyS3Action" not found
exit status 1

[fjerlov-cs]

Running on 1.227.0

➜  cli git:(feature/s3-action) ✗ go run github.com/humio/cli/cmd/humioctl actions list fjerlov-test                            
       NAME      |     TYPE      |    LABELS      
+----------------+---------------+---------------+
  webhook-action | WebhookAction | test-1,test-2  
  s3-action      | S3Action      | test           
➜  cli git:(feature/s3-action) ✗ go run github.com/humio/cli/cmd/humioctl actions show fjerlov-test s3-action
    Name | s3-action                         
    Type | S3Action                          
      ID | 2rO3izVScG2avzf7Ru2nXkVQkC5emS5X  
  Labels | test          
  ➜  cli git:(feature/s3-action) ✗ go run github.com/humio/cli/cmd/humioctl actions install fjerlov-test --file ./MyS3Action.yaml 
Successfully installed action with name: "MyS3Action"
➜  cli git:(feature/s3-action) ✗ go run github.com/humio/cli/cmd/humioctl actions show fjerlov-test MyS3Action     
    Name | MyS3Action                        
    Type | S3Action                          
      ID | 0YPj8m1Dynywvq10KuuuuCbHUq7qw57O  
  Labels | label1,label2     

[fjerlov-cs]

I had problems generating the schema (golang.org/x/tools) with Go 1.26, so I upgraded. I can keep it at 1.22.0 if needed.

[jespermbyskov]

Looking good, nothing looks odd. Someone more familiar with Go should approve.