Add HTTPClientConfig to discovery.ec2 and add a simple test

[cmbrad]

PR Description

Updates discovery.ec2 to allow specifying HTTPClientConfig fields such as proxy_url. This allows discovery.ec2 to work behind a corporate proxy.

Which issue(s) this PR fixes

Fixes #5766

Notes to the Reviewer

There are currently no tests - I've added a very basic test. It's not entirely clear to me how/where to update the docs. grafana/alloy#530 seems to relate to this.

It appears various discovery components either implement this functionality by injecting the whole HTTPClientConfig or just specific fields. I've gone with the simple implementation here.

PR Checklist

• CHANGELOG.md updated
• Documentation added
• Tests updated
• Config converters updated

[spartan0x117]

👋 Thanks for the contribution! The docs changes would go in docs/sources/flow/reference/components/discovery.ec2.md, if you could add those.

You would probably want to add a new block section with:

{{< docs/shared lookup="flow/reference/components/http-client-config-block.md" source="agent" version="<AGENT VERSION>" >}}

And you don't need to rewrite the contents 😃

[cmbrad]

Thanks for the pointer! By the look of the existing codebase (ie docs/sources/flow/reference/components/remote.http.md) that shared block works well when the options are in a separate client block - but currently I think this implementation just squashes arguments rather than using a separate block (to match the majority of other discovery component implementations).

Instead I chose to match docs/sources/flow/reference/components/discovery.consul.md (and other similar ones) which put a few select arguments directly in-line. Let me know what you think

[spartan0x117]

LGTM! Pending review from @clayton-cornell I can get this merged

[clayton-cornell]

@spartan0x117 Looks OK to me. I haven't looked into the conflicts.

[tpaschalis]

I've resolved the conflicts and will merge this as per the previous feedback.

Thanks @cmbrad!