Check for default gemfile instead on bundler directory

[smedrick]

What does this pull request do?

When the stacktrace helper attempts to find the path of installed gems, it uses a method to verify a default bundler install path that attempts to write to the filesystem. This behavior prevents the apm agent from running on a read-only filesystem. This PR attempts to keep the spirit of the functionality while getting around the need to write to the filesystem. Instead of checking if there is a default bundler path, it checks to see if there's a default gemfile.

Why is it important?

Without this bug fix, we cannot run the agent on apps in our secure k8s cluster.

Checklist

• I have signed the Contributor License Agreement.
• My code follows the style guidelines of this project (See .rubocop.yml)
• I have rebased my changes on top of the latest main branch

• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

• I have made corresponding changes to the documentation
• I have updated CHANGELOG.asciidoc
• I have updated supported-technologies.asciidoc
• Added an API method or config option? Document in which version this will be introduced

Related issues

• Closes 1464

[cla-checker-service]

❌ Author of the following commits did not sign a Contributor Agreement:
8acfac1,

Please, read and sign the above mentioned agreement if you want to contribute to this project

[estolfo]

Hi @smedrick thanks for this PR. Did you find this as the result of an error? I just wanted to see if I could reproduce it. Also, if you could sign the CLA, that'd be great.

[smedrick]

Hi @smedrick thanks for this PR. Did you find this as the result of an error? I just wanted to see if I could reproduce it. Also, if you could sign the CLA, that'd be great.

This addresses #1464

I did sign the CLA but I have no idea how it links back to the PR