42508 Rename abm to ab in API (#46657)

<!-- Add the related story/sub-task/bug number, like Resolves #123, or
remove if NA -->
**Related issue:** Resolves #42508 

Renames abm/apple_business_manager to ab/apple_business in API and
fleetctl. Uses existing renameto logic with a slight twist: added
"inline" option to handle cases particularly where a single object tree
has renames in multiple versions so that we don't break backwards
compatibiility since the default behavior when you have multi-level
renames is a new/old split at the top level

# Checklist for submitter

If some of the following don't apply, delete the relevant line.

- [x] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
See [Changes
files](https://github.com/fleetdm/fleet/blob/main/docs/Contributing/guides/committing-changes.md#changes-files)
for more information.

- [x] Input data is properly validated, `SELECT *` is avoided, SQL
injection is prevented (using placeholders for values in statements), JS
inline code is prevented especially for url redirects, and untrusted
data interpolated into shell scripts/commands is validated against shell
metacharacters.
- [x] Timeouts are implemented and retries are limited to avoid infinite
loops
- [x] If paths of existing endpoints are modified without backwards
compatibility, checked the frontend/CLI for any necessary changes

## Testing

- [x] Added/updated automated tests
- [x] Where appropriate, [automated tests simulate multiple hosts and
test for host
isolation](https://github.com/fleetdm/fleet/blob/main/docs/Contributing/reference/patterns-backend.md#unit-testing)
(updates to one hosts's records do not affect another)

- [x] QA'd all new/changed functionality manually

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Canonical Apple Business (AB) API endpoints and CLI:
/api/v1/fleet/ab_tokens, /api/v1/fleet/mdm/apple/ab_public_key, plus new
fleetctl get mdm-ab and fleetctl generate mdm-ab
  * New GitOps/config key: mdm.apple_business
* Admin UI updated to show Apple Business tokens with fleet-based
associations and updated labels

* **Deprecations**
* Legacy ABM endpoints, CLI aliases, and config keys remain supported
but emit deprecation warnings pointing to the new AB equivalents
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

server/platform/endpointer/json_key_rewriter.go

@@ -28,6 +28,15 @@ func (e *AliasConflictError) Error() string {
 type AliasRule struct {
 	OldKey string
 	NewKey string
+	// Inline opts a renamed container into "merged" response duplication:
+	// instead of the default clean split (the old key holds an all-old subtree
+	// and the new key an all-new one), the old key's subtree also carries the
+	// new-named copies of any nested renamed containers — so both names appear
+	// together on the same object. Set via the `,inline` option on the
+	// `renameto` struct tag (e.g. `renameto:"ab_tokens,inline"`). It only
+	// affects response encoding (DuplicateJSONKeys); request decoding ignores
+	// it.
+	Inline bool
 }
 
 // JSONKeyRewriteReader is a streaming io.Reader that handles
@@ -153,6 +162,8 @@ func RewriteDeprecatedKeys(data []byte, rules []AliasRule) ([]byte, map[string]s
 func RewriteOldToNewKeys(data []byte, rules []AliasRule) ([]byte, error) {
 	reversed := make([]AliasRule, len(rules))
 	for i, r := range rules {
+		// Inline is intentionally not preserved: this only renames keys, it
+		// never duplicates them.
 		reversed[i] = AliasRule{OldKey: r.NewKey, NewKey: r.OldKey}
 	}
 	result, _, err := RewriteDeprecatedKeys(data, reversed)