lib/logstorage: substitute | operator with or operator at math pipe

This is needed for avoiding confusion between the `|` operator at `math` pipe and `|` pipe delimiter.
For example, the following query was parsed unexpectedly:

   * | math foo / bar | fields x

as

   * | math foo / (bar | fields) as x

Substituting `|` with `or` inside `math` pipe fixes this ambiguity.

docs/VictoriaLogs/LogsQL.md

@@ -1799,7 +1799,7 @@ The following mathematical operations are supported by `math` pipe:
 - `arg1 % arg2` - returns the remainder of the division of `arg1` by `arg2`
 - `arg1 ^ arg2` - returns the power of `arg1` by `arg2`
 - `arg1 & arg2` - returns bitwise `and` for `arg1` and `arg2`. It is expected that `arg1` and `arg2` are in the range `[0 .. 2^53-1]`
-- `arg1 | arg2` - returns bitwise `or` for `arg1` and `arg2`. It is expected that `arg1` and `arg2` are in the range `[0 .. 2^53-1]`
+- `arg1 or arg2` - returns bitwise `or` for `arg1` and `arg2`. It is expected that `arg1` and `arg2` are in the range `[0 .. 2^53-1]`
 - `arg1 xor arg2` - returns bitwise `xor` for `arg1` and `arg2`. It is expected that `arg1` and `arg2` are in the range `[0 .. 2^53-1]`
 - `arg1 default arg2` - returns `arg2` if `arg1` is non-[numeric](#numeric-values) or equals to `NaN`
 - `abs(arg)` - returns an absolute value for the given `arg`

lib/logstorage/pipe_math.go

@@ -173,7 +173,7 @@ var mathBinaryOps = map[string]mathBinaryOp{
 		priority: 5,
 		f:        mathFuncXor,
 	},
-	"|": {
+	"or": {
 		priority: 6,
 		f:        mathFuncOr,
 	},

lib/logstorage/pipe_math_test.go

@@ -56,7 +56,7 @@ func TestPipeMath(t *testing.T) {
 		'123.45.67.89' + 1000 as ip,
 		time - time % time_step as time_rounded,
 		duration - duration % duration_step as duration_rounded,
-		(ip & ip_mask | 0x1234) xor 5678 as subnet
+		(ip & ip_mask or 0x1234) xor 5678 as subnet
 	`, [][]Field{
 		{
 			{"time_step", "30m"},