feat(http-log): support http_endpoint field to be referenceable

[vm-001]

Summary

Support http_endpoint field to be referenceable

Full changelog

• support http_endpoint field to be referenceable

Issue reference

Internal ticket FTI-4483

[vm-001]

I've not seen any vault test case for the individual plugin that uses referenceable field. So I assume that instead of adding the test case for that, Kong prefers using a single test case for vault feature(https://github.com/Kong/kong/blob/master/spec/02-integration/13-vaults/02-env_vault_spec.lua. (Correct me if I'm wrong). Thus, this PR didn't contain test case for that.

[fffonion]

Discussed with @vm-001 offline, http_endpoint doesn't make much sense to be a secrets and it doesn't
necessary meet the requirements in attached internal tickets. I would suggest to explore adding referencable
to http headers instead.

[kikito]

This change would need to be accompanied by one test

[flrgh]

Discussed with @vm-001 offline, http_endpoint doesn't make much sense to be a secrets and it doesn't necessary meet the requirements in attached internal tickets. I would suggest to explore adding referencable to http headers instead.

Removing from the 3.1 milestone per this comment. If something changes go ahead and add it back in.

[vm-001]

This change would need to be accompanied by one test

Test added. Please let me know if anything else required.

[hanshuebner]

@fffonion @vm-001 Was there a resolution to the discussion regarding making referencable http headers instead of this special-purpose functionality?

[dndx]

I remember there were discussions that question if it makes sense to make this reference able (and general concern over making too many non-secret configs referenceable).

@vm-001 do you remember the decision on this one?

[hanshuebner]

As per discussion in the planning meeting, we're not going to globally make everything referencable. We're thus going to merge this once tests pass.