[pkg/ottl] Add GetOr function to ottl.Optional

[edmocosta]

Description

The main goal of this new function is to avoid repeating the following common pattern in functions with optional arguments:

value := "foo"
if !optArgument.IsEmpty() {
    value = optArgument.Get()
}

This utility was discussed here, and would simplify the above code as:

value := optArgument.GetOr("foo")

Testing

Unit tests

[github-actions]

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[edmocosta]

Hey @evan-bradley, could you please take a look at this when you get a chance? Thanks!

[evan-bradley]

Sorry it took me so long to get to this. This looks good to me, but I think we should add an API changelog entry.