Support ALTER SYSTEM

Summarize the changes

• wip: alter system

ALTER SYSTEM
SET configuration_parameter { TO | = } { value | DEFAULT }
[ FOR ALL [ TIERS ] | FOR TIER tier ]

Closes #628 (closed).

Ensure that

• New code is covered by unit and integration tests.
• Related issues would be automatically closed with gitlab's closing pattern (Closes #1, #2).
• Public modules are documented (check the rendered version with cargo doc --open).
• (if PEST grammar is changed) EBNF grammar reflects these changes (check the result with railroad diagram generator.

Next steps

• Cherry-pick to: none
• Update sbroad submodule in picodata/picodata.
• (if EBNF grammar is changed) create a follow-up issue in picodata/docs.