fix(configuration-hydrator): use custom SSL configuration from env

This makes sure we use configuration provided via env variables. Previously, it would be assigned
incorrectly.

src/__mocks__/fs.ts

@@ -0,0 +1,7 @@
+'use strict';
+
+module.exports = {
+	readFileSync() {
+		return 'file-contents'
+	}
+};

src/__tests__/ConfigurationHydrator.spec.ts

@@ -1,5 +1,7 @@
 import { ConfigurationHydrator } from '../lib/ConfigurationHydrator'
 
+jest.mock('fs');
+
 process.env.ZEEBE_NODE_LOG_LEVEL = process.env.ZEEBE_NODE_LOG_LEVEL || 'NONE'
 // const gatewayAddress = process.env.ZEEBE_GATEWAY_ADDRESS || '0.0.0.0:26500'
 
@@ -15,6 +17,9 @@ const ENV_VARS_TO_STORE = [
 	'ZEEBE_CLIENT_MAX_RETRIES',
 	'ZEEBE_CLIENT_RETRY',
 	'ZEEBE_CLIENT_MAX_RETRY_TIMEOUT',
+	'ZEEBE_CLIENT_SSL_ROOT_CERTS_PATH',
+	'ZEEBE_CLIENT_SSL_PRIVATE_KEY_PATH',
+	'ZEEBE_CLIENT_SSL_CERT_CHAIN_PATH',
 ]
 
 beforeAll(() => {
@@ -370,6 +375,21 @@ test('Can be unsecured via the environment', () => {
 	const conf = ConfigurationHydrator.configure('localhost:26600', {})
 	expect(conf.useTLS).toBe(true)
 })
+test('Cert chain path can be configured via the environment', () => {
+	process.env.ZEEBE_CLIENT_SSL_CERT_CHAIN_PATH = '/my/path'
+	const conf = ConfigurationHydrator.configure('localhost:26600', {})
+	expect(conf.customSSL?.certChain).toBe('file-contents')
+})
+test('Private key path can be configured via the environment', () => {
+	process.env.ZEEBE_CLIENT_SSL_PRIVATE_KEY_PATH = '/my/path'
+	const conf = ConfigurationHydrator.configure('localhost:26600', {})
+	expect(conf.customSSL?.privateKey).toBe('file-contents')
+})
+test('Root certs path can be configured via the environment', () => {
+	process.env.ZEEBE_CLIENT_SSL_ROOT_CERTS_PATH = '/my/path'
+	const conf = ConfigurationHydrator.configure('localhost:26600', {})
+	expect(conf.customSSL?.rootCerts).toBe('file-contents')
+})
 test('Retry can be configured via the environment', () => {
 	process.env.ZEEBE_CLIENT_RETRY = 'false'
 	const conf = ConfigurationHydrator.configure('localhost:26600', {})

src/lib/ConfigurationHydrator.ts

@@ -86,18 +86,23 @@ export class ConfigurationHydrator {
 		}
 	}
 
-	private static readCustomSSLFromEnvironment(): Partial<CustomSSL> {
+	private static readCustomSSLFromEnvironment(): { customSSL: Partial<CustomSSL> } {
 		const rootCerts = ConfigurationHydrator.ENV()
 			.ZEEBE_CLIENT_SSL_ROOT_CERTS_PATH
 		const certChain = ConfigurationHydrator.ENV()
 			.ZEEBE_CLIENT_SSL_CERT_CHAIN_PATH
 		const privateKey = ConfigurationHydrator.ENV()
 			.ZEEBE_CLIENT_SSL_PRIVATE_KEY_PATH
-		return {
+
+		const customSSL = {
 			certChain: certChain ? fs.readFileSync(certChain) : undefined,
 			privateKey: privateKey ? fs.readFileSync(privateKey) : undefined,
 			rootCerts: rootCerts ? fs.readFileSync(rootCerts) : undefined,
 		}
+
+		return {
+			customSSL,
+		}
 	}
 
 	private static readOAuthFromEnvironment(