[E2E][Testing] Update E2E tests to use full auth stack (PATH+GUARD)

[commoddity]

Objective

Run PATH E2E tests against PATH+GUARD (Envoy Gateway) for a full E2E request flow that includes auth, rate limiting, etc.

Origin Document

Current PATH E2E tests run against a standalone PATH binary. While this does give good confidence in all the core logic of PATH's request handling, it does not test the request authorization logic (ie. API key, JWT, or Grove-specific auth).

NOTE

This work will likely be made much easier by building off the localnet dev container work done in PR:
#225

Goals

• E2E tests provide the option to include GUARD in test stack setup
• E2E tests include configuration of request auth (ie. API key, JWT, Portal App ID & Secret Key)
• E2E tests are easy to spin up using Tilt and the full stack is self contained

Deliverables

• Local & CI solution
• Test code modified to send request against Envoy gateway
• Test code modified to configure requests with auth headers, etc.

Non-goals / Non-deliverables

• Infrastructure related E2E testing (this will be handled separately)

General deliverables

• Comments: Add/update TODOs and comments alongside the source code so it is easier to follow.
• Testing: Add new tests (unit and/or E2E) to the test suite.
• Makefile: Add new targets to the Makefile to make the new functionality easier to use.
• Documentation: Update architectural or development READMEs; use mermaid diagrams where appropriate.

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Creator: @commoddity
Co-Owners: @adshmh @Olshansk