Extend pre-checks. Misc. Improvements: escape $, support arrays in pre_sql and workload_sql; support empty arrays

Make sure that the options are specified in the correct format:

• option=value in the 'pre_configs' option, and is an array.
• The pgbench utility is specified in the 'workload_pgbench' option.
  • It is difficult to fully check the syntax of the command being executed without actually executing it. Therefore, we are adding only a basic check for the presence of the pgbench command.
  • Note: Analyze the result after executing the test.
• SQL statement in the 'pre_sql' and 'workload_sql' options.
  • Skip it. It would be extremely difficult and inefficient to create a full-fledged SQL parser in a Bash script, given the complexity of the SQL syntax and the variety of possible commands and constructs.
  • Note: Analyze the result after executing the test.

Improvements

• Support for an empty array in pre_configs
  • Execute commands only if the array is not empty
  • Fixed: https://gitlab.com/postgres-ai/postgresql-consulting/tests-and-benchmarks/-/jobs/5855245322
• Support for newline characters in SQL
  • Escape newline characters in TEST_RUNS variable, and delete newline characters in 'pre_sql' and 'workload_sql' options.
  • Fixed: https://gitlab.com/postgres-ai/postgresql-consulting/tests-and-benchmarks/-/jobs/5839732812
• Support for DO blocks in SQL
  • Added a workaround for CI pipelines where the '$$' symbol is not properly escaped
• Support for arrays in pre_sql and workload_sql
  • Fixed: https://gitlab.com/postgres-ai/postgresql-consulting/tests-and-benchmarks/-/jobs/5848711947