[pkg/ottl] Mathematical Expressions are able to handle time.Time and time.Duration types.

[TylerHelmuth]

In order to support complex interactions with time we need to support the following cases in our mathematical expressions:

• Subtracting a time.Time from time.Time must result in a time.Duration.
• Adding a time.Duration to a time.Time must result in a time.Time
• Subtracting a time.Duration from a time.Time must result in a time.Time
• Adding a time.Duration to a time.Duration must result in a time.Duration
• Subtracting a time.Duration from a time.Duration must result in a time.Duration

Only these type interactions should be supported. For example, the following SHOULD NOT be allowed:

• adding/subtracting an integer from a time.Time.
• adding/subtracting an integer from a time.Duration.

At the moment these rules cannot be enforced by the grammar, instead we will have to enforce these rules in the execution of the mathematical expressions. This is the existing pattern we use for other type checking.

[kamalmarhubi]

Does this mean adding time.Duration as the difference type?

[TylerHelmuth]

I will detail these cards next week, but yes.

[github-actions]

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