Align agents on ext vs external

[roncohen]

We need to align on whether we're using ext or external for span.type:

cc @elastic/apm-agent-devs

I suggest we use external instead of ext. There's no reason to use the abbreviation.
That means Node agent, Ruby agent and Python agent needs to change from ext to external.

[vigneshshanmugam]

Since RUM agent is not listed here, Confirming that RUM agent uses external for all API(XHR and FETCH) calls.

[felixbarny]

I don't mind either but I agree we should align. The Java agent implemented it according to https://docs.google.com/spreadsheets/d/1SmWeX5AeqUcayrArUauS_CxGgsjwRgMYH4ZY8yQsMhQ which only mentions external.

[gregkalapos]

I suggest we use external instead of ext.

In .NET we already follow this. Similar to Java, we implemented it based on the spreadsheet.

[roncohen]

Created issues for Node, Ruby and Python agents now. Links above ^

[mikker]

@roncohen Would this be a breaking change?

[beniwohli]

FWIW, I consider it a breaking change and will bump the major version of the python agent to 5 (which conveniently also allows me to do a few other breaking changes)