Update dependency com.github.hmcts:send-letter-client to v5

Author: renovate[bot]

Diff for: build.gradle

@@ -270,7 +270,7 @@ dependencies {
   implementation group: 'com.github.hmcts', name: 'ccd-client', version: '5.0.3'
   implementation group: 'com.github.hmcts', name: 'idam-java-client', version: '3.0.3'
   implementation group: 'com.github.hmcts', name: 'java-logging', version: '6.1.6'
-  implementation group: 'com.github.hmcts', name: 'send-letter-client', version: '4.0.4'
+  implementation group: 'com.github.hmcts', name: 'send-letter-client', version: '5.0.1'
   implementation group: 'com.github.hmcts', name: 'service-auth-provider-java-client', version: '5.2.0'
   implementation group: 'com.github.hmcts', name: 'ccd-case-document-am-client', version: '1.7.3'