[ES|QL] automate Elasticsearch grammar sync with a buildkite pipeline

[drewdaemon]

Steps

• provision a pipeline in terraform
  • need to use a buildkite_pipeline along with a pipeline_schedule
• add script to https://github.com/elastic/kibana/tree/main/.buildkite/scripts
  • check out Elasticsearch and Kibana main (may already be available on host)
  • copy elasticsearch/x-pack/plugin/esql/src/main/antlr/EsqlBaseLexer.g4 to kibana/packages/kbn-monaco/src/esql/antlr/esql_lexer.g4
  • inject
    • license header
    • new grammar name
    • options { caseInsensitive = true; }
  • check git diff
  • if any diff, commit and open PR via GH API
• add pipeline to https://github.com/elastic/kibana/tree/main/.buildkite/pipelines

[drewdaemon]

Blocked on #178423

[drewdaemon]

ANTLR is now available in CI. Removing blocked label

[drewdaemon]

Done!