AIP-38 | Add Task Instance XCom

[bbovenzi]

Once #44656 we will have a tab on the task instance details page to show XComs. We should use the public API to render a table of all xcoms for that task instance.

[tirkarthi]

@bbovenzi I can take this up if you are okay. The API returns only XCom keys and there needs to be an API call per XCom entry to get the value as string. There could also be a clipboard button to copy the contents of the xcom entry.

[tirkarthi]

Created #44869 as a first attempt.