aws_resiliencehubv2_service: Add 'associated_system' configuration block

[hwkiem]

Rollback Plan

If a change needs to be reverted, we will publish an updated version of the library.

Changes to Security Controls

No changes to security controls in this pull request.

Description

Adds the associated_system configuration block to the aws_resiliencehubv2_service resource, and the matching computed attribute to its data source, so a service can be associated with a system.

The API has no Associate* operation — the relationship is a field on the service (AssociatedSystems on CreateService/UpdateService), so it is modelled as an argument, like the existing policy_arn.

Notes for reviewers:

• UpdateService treats an omitted AssociatedSystems as "no change", so Update sends an explicitly empty list when the last block is removed. Without this, removing every block applies cleanly but leaves the systems associated in AWS, and the next refresh plans them straight back — verified against the API, and covered by the third step of TestAccResilienceHubV2Service_associatedSystem.
• AssociatedSystem.UserJourneyIds is deferred until aws_resiliencehubv2_user_journey (F resiliencehubv2 user journey #48330) lands. Using a block rather than a flat set of ARNs keeps adding it additive.
• The aws_resiliencehubv2_system sweeper now depends on the service sweeper, since DeleteSystem can fail while an associated service exists.

I understand the author of #48330 may intend to cover system association there. As of its current diff that PR does not touch AssociatedSystems, so this is raised to be taken or left as the maintainers prefer — happy to close it if it is better folded into the user journey work.

Relations

Closes #49475
Relates #48122
Relates #48330

References

• AssociatedSystem data type

Output from Acceptance Testing

% make testacc TESTS=TestAccResilienceHubV2Service_ PKG=resiliencehubv2
TF_ACC=1 go1.26.5 test ./internal/service/resiliencehubv2/... -v -count 1 -parallel 20 -run='TestAccResilienceHubV2Service_'  -timeout 360m -vet=off -buildvcs=false
--- PASS: TestAccResilienceHubV2Service_Tags_DefaultTags_nullNonOverlappingResourceTag (63.39s)
--- PASS: TestAccResilienceHubV2Service_Tags_DefaultTags_nullOverlappingResourceTag (63.59s)
--- PASS: TestAccResilienceHubV2Service_Tags_DefaultTags_emptyProviderOnlyTag (63.65s)
--- PASS: TestAccResilienceHubV2Service_disappears (82.96s)
--- PASS: TestAccResilienceHubV2Service_Tags_DefaultTags_emptyResourceTag (88.47s)
--- PASS: TestAccResilienceHubV2Service_policyARN (89.21s)
--- PASS: TestAccResilienceHubV2Service_Tags_ComputedTag_onCreate (94.45s)
--- PASS: TestAccResilienceHubV2Service_regions (95.58s)
--- PASS: TestAccResilienceHubV2Service_Tags_ComputedTag_OnUpdate_replace (101.68s)
--- PASS: TestAccResilienceHubV2Service_Tags_EmptyTag_OnUpdate_replace (110.87s)
--- PASS: TestAccResilienceHubV2Service_Tags_ComputedTag_OnUpdate_add (111.17s)
--- PASS: TestAccResilienceHubV2Service_Identity_basic (120.40s)
--- PASS: TestAccResilienceHubV2Service_dependencyDiscovery (123.10s)
--- PASS: TestAccResilienceHubV2Service_kmsKeyID (59.75s)
--- PASS: TestAccResilienceHubV2Service_description (123.79s)
--- PASS: TestAccResilienceHubV2Service_associatedSystem (134.71s)
--- PASS: TestAccResilienceHubV2Service_Tags_DefaultTags_updateToResourceOnly (135.82s)
--- PASS: TestAccResilienceHubV2Service_Tags_null (72.84s)
--- PASS: TestAccResilienceHubV2Service_Tags_IgnoreTags_Overlap_resourceTag (140.15s)
--- PASS: TestAccResilienceHubV2Service_List_includeResource (53.77s)
--- PASS: TestAccResilienceHubV2Service_List_regionOverride (46.62s)
--- PASS: TestAccResilienceHubV2Service_Tags_IgnoreTags_Overlap_defaultTag (149.38s)
--- PASS: TestAccResilienceHubV2Service_Tags_emptyMap (62.59s)
--- PASS: TestAccResilienceHubV2Service_List_basic (42.16s)
--- PASS: TestAccResilienceHubV2Service_basic (48.15s)
--- PASS: TestAccResilienceHubV2Service_Tags_DefaultTags_nonOverlapping (171.43s)
--- PASS: TestAccResilienceHubV2Service_Tags_DefaultTags_overlapping (171.50s)
--- PASS: TestAccResilienceHubV2Service_Tags_addOnUpdate (84.16s)
--- PASS: TestAccResilienceHubV2Service_Tags_EmptyTag_onCreate (90.76s)
--- PASS: TestAccResilienceHubV2Service_Tags_EmptyTag_OnUpdate_add (117.14s)
--- PASS: TestAccResilienceHubV2Service_Tags_DefaultTags_updateToProviderOnly (70.13s)
--- PASS: TestAccResilienceHubV2Service_Identity_regionOverride (65.90s)
--- PASS: TestAccResilienceHubV2Service_tags (113.81s)
--- PASS: TestAccResilienceHubV2Service_Tags_DefaultTags_providerOnly (107.44s)
PASS
ok  	github.com/hashicorp/terraform-provider-aws/internal/service/resiliencehubv2	223.688s

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