feat: databend-meta transaction support generic bool-expression and else-if chain

[drmingdrmer]

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Summary

feat: databend-meta transaction support generic bool-expression and else-if chain

Since this commit, application is allowed to specify a complex bool
expressions as the transaction predicate.

For example, the transaction will execute as if running the following
pseudo codes:

if (a == 1 || b == 2) && (x == 3 || y == 4) { ops1 }
else if (x == 2 || y == 1) { ops2 }
else if (y == 3 && z == 4) { ops3 }
else { ops4 }

let eq = |key: &str, val: &str| TxnCondition::eq_value(sample(key), b(val));

TxnRequest{
    operations: vec![
                BoolExpression::new(
                    Some(eq("a", 1).or(eq("b", 2))
                         .and(eq("x", 3).or(eq("y", 4)))),
                    ops1),
                BoolExpression::new(
                    Some(eq("x", 2).or(eq("y", 1))),
                    ops2),
            ],

    condition: vec![eq("y", 3), eq("z", 4)],
    if_then: ops3,
    else_then: ops4, 
}

For backward compatibility, both already existing condition and the new
operations will be evaluated: transaction handler evaluate the
operations first. If there is a met condition, execute and return.
Otherwise, it evaluate condition and then execute if_then branch or
else_then branch.

TxnReply changes:

Add field execution_path to indicate the executed branch, which is one
of:

• "operation:<index>", operation at index is executed.
• "then": if_then is executed.
• "else": else_then is executed.

TxnReply.success is set to false only when else is executed.

Tests

• Unit Test
• Logic Test
• Benchmark Test
• No Test - Explain why

Type of change

• New Feature (non-breaking change which adds functionality)

Related Issues

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This change is 

[zhang2014]

👍