feat(providers/aws): rich self-describing RI display names (closes #687)

[cristim]

Summary

• EC2: tagReservedInstance now stamps a self-describing Name tag using BuildReservationName (format ec2-{region}-{sku}-{count}x-{term}-{paymt}-{ts}-{rand}). EC2 PurchaseReservedInstancesOfferingInput has no customer-supplied name field, so the Name tag is the only way to identify the RI in the AWS console without querying CUDly's purchase history. Count, Term, and PaymentOption descriptor tags are also added to match the Redshift tag set.
• Redshift: tagReservedNode gains the same Name tag via BuildReservationName (format redshift-{region}-{sku}-...). Same rationale: no customer-supplied ID on PurchaseReservedNodeOfferingInput.
• RDS / ElastiCache / MemoryDB / OpenSearch: already wired to BuildReservationName as the customer-supplied reservation ID in prior work on this branch; no changes needed.
• Also fixes 3 pre-existing test compile errors (findOfferingID called with 2 args instead of 3 in rds and redshift test files).

Format

{svc}-{region}-{sku}-{count}x-{term}-{paymt}-{ts}-{rand} (60-char cap via BuildReservationName in pkg/common), e.g.:

ec2-us-west-2-m5-xlarge-3x-1yr-allup-20260522T190000-a1b2c3d4
redshift-eu-central-1-ra3-4xlarge-1x-1yr-noup-20260522T190000-a1b2c3d4

Services wired (7 total)

Service	Mechanism
EC2	Name tag in tagReservedInstance (post-purchase CreateTags)
Redshift	Name tag in tagReservedNode (post-purchase CreateTags)
RDS	rich ReservedDBInstanceId (already done in branch)
ElastiCache	rich ReservedCacheNodeId (already done in branch)
MemoryDB	rich ReservationId (already done in branch)
OpenSearch	rich ReservationName (already done in branch)
Savings Plans	N/A (SP uses a UUID offering ID; no per-purchase name field)

Test plan

• go build ./... passes (verified locally)
• TestClient_tagReservedInstance_NameTagPresent - asserts Name tag present and self-describing on EC2 CreateTags call
• TestClient_PurchaseCommitment_NameTagInCreateTagsRequest - end-to-end EC2 purchase asserts Name tag in CreateTags
• TestClient_tagReservedNode_NameTagPresent - asserts Name tag present on Redshift CreateTags call
• TestClient_PurchaseCommitment_TagsCarryRichDescriptors (extended) - asserts Name tag starts with "redshift" in addition to Count/Term/PaymentOption
• All 425 tests in affected packages pass (ec2, redshift, rds, elasticache, memorydb, opensearch, pkg/common)

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

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Run ID: 72a14f55-1a00-4ac0-ab9c-e1fc5240b14b

📥 Commits

Reviewing files that changed from the base of the PR and between 4956d66 and bd68fd9.

📒 Files selected for processing (5)

• providers/aws/services/ec2/client.go
• providers/aws/services/ec2/client_test.go
• providers/aws/services/rds/client_test.go
• providers/aws/services/redshift/client.go
• providers/aws/services/redshift/client_test.go

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• Create PR with unit tests
• Commit unit tests in branch fix/687-wave4

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