feat: client spec to support deltaApi (#9222)

Add client spec version for delta API.

Author: sjaanus

src/lib/services/client-spec-service.ts

@@ -5,7 +5,7 @@ import semver, { type SemVer } from 'semver';
 import BadDataError from '../error/bad-data-error';
 import { mustParseStrictSemVer, parseStrictSemVer } from '../util/semver';
 
-export type ClientSpecFeature = 'segments';
+export type ClientSpecFeature = 'segments' | 'deltaApi';
 
 export class ClientSpecService {
     private readonly logger: Logger;
@@ -14,6 +14,7 @@ export class ClientSpecService {
 
     private readonly clientSpecFeatures: Record<ClientSpecFeature, SemVer> = {
         segments: mustParseStrictSemVer('4.2.0'),
+        deltaApi: mustParseStrictSemVer('5.2.0'),
     };
 
     constructor(config: Pick<IUnleashConfig, 'getLogger'>) {