allowed observable in PipeTransform configuration of TableColumn options

[souzara]

What kind of change does this PR introduce? (check one with "x")

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior? (You can also link to an open issue here)
Just synchronous transform works in PipeTransform of TableColumn Options.

What is the new behavior?
Added optional feature, if a pipe that returns a Observable in transform method, it's will be subscribed and set value that the observable returns.

Does this PR introduce a breaking change? (check one with "x")

• Yes
• No

If this PR contains a breaking change, please describe the impact and migration path for existing applications: ...

Other information:

[amcdnl]

You never unsubscribe from this, I think this would create a memory leak.

[souzara]

What do you think about something like this:

let pipeSubscription = observable.subscribe((transformedValue) => {
value = transformedValue;
pipeSubscription.unsubscribe();
});

well anyway if observable never call "next" in observer, "pipeSubscription.unsubscribe()" never will be called.

I can add it in a array of subscriptions, then in ngDestroy, we can unsubscribe for all...