feat: upgrade go agent to v2

[kruskall]

What does this PR do?

go.elastic.co/apm v1 has been deprecated for a while. Update the dependency to v2.

Why is it important?

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have run the Unit tests (make unit-test), and they are passing locally
• I have run the End-2-End tests for the suite I'm working on, and they are passing locally
• I have noticed new Go dependencies (run make notice in the proper directory)

Author's Checklist

• [ ]

How to test this PR locally

Related issues

[mergify]

This pull request does not have a backport label. Could you fix it @kruskall? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v./d./d./d is the label to automatically backport to the 7./d branch. /d is the digit
  NOTE: backport-skip has been added to this pull request.

[cmacknz]

This is a surprising number of additional dependencies.

[kruskall]

This is caused by module pruning (https://go.dev/ref/mod#graph-pruning) introduced in go 1.17.

The dependencies listed here are indirect dependencies. They were always there in a sense but now they are explicitly mentioned in go.mod because go is pruning unnecessary transitive dependencies.
This is also the reason why the go.sum has way entries.

[cmacknz]

Ah I only skimmed this and missed the // indirect. Thanks!

[cmacknz]

Changes look good, the large number of additional dependencies in go.mod is a bit suspicious though.