align elasticsearch body capturing with other agents

[beniwohli]

See elastic/apm#55

This also allows us to get rid of a hack we used to pass the API method
and an unserialized version of the body to the instrumentation. Neither
is used anymore, so we can skip that part of the instrumentation.

This does also mean that we stop capturing the body for some methods,
specifically update and delete_by_query.

closes #419

[beniwohli]

@basepi @felixbarny I guess strictly speaking this could constitute a backwards incompatible change, so I vote for including this in 6.0, not 5.10.1. What do you think?

[felixbarny]

@trentm has been advocating for having the list of endpoints that we capture bodies for be configurable.

This does also mean that we stop capturing the body for some methods,
specifically update and delete_by_query.
I guess strictly speaking this could constitute a backwards incompatible change

Would the backwards compatibility be remained if you just included */delete_by_query and */_update/* to the URL patterns that have body capturing enabled?
This would enable us to merge the new code in now as opposed to the 6.x branch at the expense of being slightly out-of-sync with what the other agents are doing. But in 6.0, we could just remove the patterns again or decide to add them to the default lists of other agents.

For these things, I sometimes struggle to find a clear border of what's considered backwards incompatible. In general, I think we should be able to fine-tune the amount of data we collect without having to major-bump the agent version.
Maybe in this case it's fine to remove the delete_by_query and update APIs from the default list as long as there's a config option for users to re-enable them.

[apmmachine]

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[beniwohli]

@felixbarny 6.0 isn't very far away, probably just a couple of weeks.

As for including those two endpoints, at least for update, we previously only captured the script part of the body (for reasons that I'm sure made sense at the time). If at all possible, I want to avoid adding that back, since we then need to introduce that ugly hack again (or re-parse the already serialized JSON body).

[felixbarny]

6.0 isn't very far away, probably just a couple of weeks.

ah, nvm then