geolocation: remove CLI flags for targets, parents, and allowed keys

[ben-dz]

Resolves: #3453

Summary of Changes

• Remove --additional-parent, --additional-targets, --additional-icmp-targets, --allowed-pubkeys from geoprobe-agent now that onchain configuration is working
• Remove --additional-child-probes from telemetry-agent
• Remove all CLI-to-onchain merge logic from discovery layers — targets, parents, and allowed keys now come exclusively from onchain state
• Remove ParseProbeAddresses and ParseICMPProbeAddresses (no longer needed)
• E2E tests adopt geolocation: add ICMP target E2E test and refactor geoprobe container management #3454's refactored helpers (which already removed CLI flag usage)

Depends on: #3454 (e2e container refactoring). The e2e/geoprobe_test.go file is taken from #3454's head to avoid conflicts at merge time.

Diff Breakdown

Category	Files	Lines (+/-)	Net
Core logic	9	+37 / -415	-378
Tests	6	+87 / -527	-440
E2E (#3454)	1	+159 / -174	-15

Heavily deletion-weighted: removes ~800 lines of CLI plumbing and merge logic that onchain discovery makes unnecessary.

Key files (click to expand)

• controlplane/telemetry/cmd/geoprobe-agent/main.go — removed 4 flag defs, parentDZD struct, parse helpers, all CLI wiring
• controlplane/telemetry/internal/geoprobe/address.go — removed ParseProbeAddresses, ParseICMPProbeAddresses
• controlplane/telemetry/internal/geoprobe/target_discovery.go — removed CLI fields from config/struct, removed mergeKeys, simplified discover()
• controlplane/telemetry/internal/geoprobe/onchain_discovery.go — removed CLIParents, CLI merge logic, renamed cliOnlyUpdate → emptyUpdate
• controlplane/telemetry/internal/geoprobe/discovery.go — removed InitialProbes, mergeProbes
• controlplane/telemetry/internal/telemetry/collector.go — simplified geoprobe init to GeolocationClient != nil
• controlplane/telemetry/cmd/telemetry/main.go — removed --additional-child-probes flag and parsing

Testing Verification

• Unit tests pass for geoprobe and telemetry packages (including updated tests for discovery, coordinator, config validation)
• TestE2E_GeoprobeOnchainTargets passes end-to-end (parent discovery, outbound TWAMP + ICMP measurement, inbound signed TWAMP probing) with onchain-only configuration
• E2E test build verified with -tags e2e

[nikw9944]

Review Summary

Clean removal of CLI override flags (--additional-parent, --additional-targets, --additional-icmp-targets, --allowed-pubkeys, --additional-child-probes) from the geoprobe-agent and telemetry-agent, shifting all configuration to onchain state via parent and target discovery.

The PR is well-scoped: 17 files changed, ~1087 lines removed, ~123 added. All references to the removed flags, struct fields (CLIParents, CLITargets, CLIIcmpTargets, CLIAllowedKeys, InitialChildGeoProbes, InitialProbes), parsing functions (parseParentDZD, parseAllowedPubkeys, ParseProbeAddresses, ParseICMPProbeAddresses), and merge helpers (mergeProbes, mergeKeys) are fully cleaned up — no stale references remain.

Verification

• All tests pass: geoprobe-agent (0.28s), geoprobe internal (105s), telemetry (9.1s)
• Both binaries compile cleanly
• Grep across the telemetry tree confirms zero remaining references to any removed identifiers

Notes

• The signed TWAMP reflector now starts with nil authorized keys and gets populated solely via SetAuthorizedKeys from the target discovery channel — this is correct since the reflector's LinuxReflector handles nil gracefully.
• The collector.go simplification (gating geoprobe coordinator on GeolocationClient != nil instead of also checking InitialChildGeoProbes) is a clean consequence of the removal and correctly flattens the previously nested conditional.
• Test updates properly adapt to the new initialization model (e.g., TestCoordinator_HandleProbeUpdate_Remove now seeds probes via handleProbeUpdate instead of InitialProbes).
• CHANGELOG entry is accurate and complete.

No issues found.