Using the else keyword shouldn't always requires a body

[patrick-east]

Expected Behavior

Any other rule body can be omitted with an implicit { true } being used for evaluation.

Ex:

p = 1

really means

p = 1 {
    true
}

So for else rule bodies this should also work..

p = 1 {
    input.x == "foo"
} else = -1

Should mean..

p = 1 {
    input.x == "foo"
} else = -1 {
    true
}

Actual Behavior

The body for the else rule is required:

$ opa parse /tmp/x.rego
1 error occurred: /tmp/x.rego:6: rego_parse_error: no match found
	} else = -1
	          ^

Additional Info

We should be able to just apply the same logic we do for any other rule body for these.