Provide examples of the conditional operator

[benjaminapetersen]

Change
It took several passes over the documentation and some experimentation to realize that a basic "if" statement is indeed easy to write in CEL simply using logical operators. Given that CEL is a golang project and has roots in the kubernetes community as well, clarifying that the lack of an "if" statement does not mean it is unable to perform this type of logic would be ideal.

Example

CEL does not have an "if" statement, however, similar decision making flows are trivial to perform using its built-in logical operators. For example:

expr:  'firstName != "bob" ? firstName + ":" + lastName : firstName'

Understanding that CEL can perform simple conditional logic and return one value or another was not immediately obvious.

Alternatives considered
Briefly list alternative designs, or an example of the functionality to be replaced.

[TristonianJones]

@benjaminapetersen I think this is a good example to include in the github.com/google/cel-spec

The ternary operator isn't quite an if statement since a classic if statement doesn't guarantee a return value; however, you can mimic if-else and if-elseif-... flows this way.