Docs: fixing maven build erros

[INFO] — asciidoctor-maven-plugin:2.0.0-RC.1:process-asciidoc (html) @ infinispan-docs —
...
[INFO] asciidoctor: INFO: possible invalid reference: protostream_cm_config
[INFO] asciidoctor: INFO: possible invalid reference: _configuration
[INFO] asciidoctor: WARN: topics/transactions.adoc: line 2: id assigned to section already in use: transactions
[INFO] asciidoctor: INFO: possible invalid reference: _building_infinispan
[INFO] asciidoctor: INFO: possible invalid reference: _comments
[INFO] asciidoctor: ERROR: titles/server/stories.adoc: line 9: include file not found: /home/dnaro/git/infinispan/documentation/src/main/asciidoc/stories/assembly_server_single_port.adoc
[INFO] asciidoctor: WARN: topics/con_memcached_client_encoding.adoc: line 2: section title out of sequence: expected level 2, got level 3