feat: implement AST

src/errors.rs

src/frontend.rs

src/frontend/sql.rs

src/frontend/sql/ast.rs

src/frontend/sql/ast/tests.rs

src/frontend/sql/grammar.pest

src/lib.rs

tests/artifactory/frontend/sql/simple_query.yaml

tests/artifactory/frontend/sql/transform_select_2.yaml

tests/artifactory/frontend/sql/transform_select_3.yaml

tests/artifactory/frontend/sql/transform_select_4.yaml

tests/artifactory/frontend/sql/transform_select_5.yaml