feat: add IAM OIDC provider tagging actions

Adds `TagOpenIDConnectProvider`, `UntagOpenIDConnectProvider` and `ListOpenIDConnectProviderTags` to the standalone IAM service, backed by both the internal and Vault storers. They follow the user and role tagging actions in most respects — the tag action merges into the provider's existing tags and rejects a repeated key, untag removal is idempotent, and the tag listing is sorted by key and paginated, with the per-request member count and the per-provider tag total enforced as separate quotas so replacing a tag on a provider already at the 50-tag cap still succeeds — but differ in the one respect IAM itself draws: OIDC provider tag keys are compared exactly, not case-insensitively. On a provider `env` and `ENV` are two independent tags, both may be supplied in a single request, only a byte-identical repeat is a duplicate (reported without the "Tag keys are case insensitive" note the user and role actions carry), and untagging `env` leaves `ENV` in place.

That distinction is now carried by `iamutil.TagKeyCase`, which `ParseTags` uses for duplicate detection and which `mergeTags`, `removeTags` and the tag listing's marker lookup use for key matching. `CreateOpenIDConnectProvider` moves onto the exact comparison too, so a provider created with case-differing tag keys keeps both.

All three actions are authorized against the target provider's ARN, so `aws:ResourceTag/<key>` reads the provider's own tags, and the tag and untag actions populate `aws:RequestTag/<key>` and `aws:TagKeys` respectively, so a tag-scoped policy Condition governs which tags a caller may set or remove. All three report a missing provider with the wording `DeleteOpenIDConnectProvider` uses rather than the one `GetOpenIDConnectProvider` uses, which is why the Vault provider read now takes the not-found error its calling action reports.

The WebGUI gains a Tags section in the OIDC provider manage view, replacing the read-only tag row, and the shared tag editor gains a case-sensitive mode that changes its duplicate-key check, its diffing of an edited set into an untag and tag pair, and the wording of its guidance.

iamapi/internal/iammiddleware/policy.go

@@ -186,7 +186,8 @@ func resourceForAction(ctx fiber.Ctx, store iamutil.IdentityStore, action string
 	case "CreateOpenIDConnectProvider":
 		return newOIDCProviderResource(ctx), nil
 	case "GetOpenIDConnectProvider", "DeleteOpenIDConnectProvider", "AddClientIDToOpenIDConnectProvider",
-		"RemoveClientIDFromOpenIDConnectProvider", "UpdateOpenIDConnectProviderThumbprint":
+		"RemoveClientIDFromOpenIDConnectProvider", "UpdateOpenIDConnectProviderThumbprint",
+		"TagOpenIDConnectProvider", "UntagOpenIDConnectProvider", "ListOpenIDConnectProviderTags":
 		arn, _ := iamutil.RequestParam(ctx, "OpenIDConnectProviderArn")
 		if arn == "" {
 			return "", nil
@@ -382,9 +383,11 @@ func requestConditionContext(ctx fiber.Ctx, identity types.Identity, action stri
 	}
 
 	switch action {
-	case "CreateUser", "CreateRole", "CreateOpenIDConnectProvider", "TagUser", "TagRole":
-		addRequestTagContext(condCtx, ctx)
-	case "UntagUser", "UntagRole":
+	case "CreateUser", "CreateRole", "TagUser", "TagRole":
+		addRequestTagContext(condCtx, ctx, iamutil.TagKeysFolded)
+	case "CreateOpenIDConnectProvider", "TagOpenIDConnectProvider":
+		addRequestTagContext(condCtx, ctx, iamutil.TagKeysExact)
+	case "UntagUser", "UntagRole", "UntagOpenIDConnectProvider":
 		addTagKeysContext(condCtx, ctx)
 	}
 
@@ -459,8 +462,8 @@ func addPrincipalTagContext(condCtx map[string][]string, tags []types.Tag) {
 // the same parse independently and will reject the request with the
 // specific tag-validation error afterward, so no write can succeed with
 // tags that silently evaded a tag-scoped Condition.
-func addRequestTagContext(condCtx map[string][]string, ctx fiber.Ctx) {
-	tags, err := iamutil.ParseTags(ctx)
+func addRequestTagContext(condCtx map[string][]string, ctx fiber.Ctx, keyCase iamutil.TagKeyCase) {
+	tags, err := iamutil.ParseTags(ctx, keyCase)
 	if err != nil || len(tags) == 0 {
 		return
 	}