bugfix: path-based header injection

[jranson]

This is a major overhaul of how Paths work, along with standardization of all *Options using a ConfigOptions interface.

• a Backend Options's Path Options member is now a slice instead a map, to ensure repeatable order parsing. Paths no longer need to be named.
• Custom path options now work using an updated Overlay function fixes Custom paths not effective #671
• All Options now have standard Validate, Initialize and Clone functions from the ConfigOptions interface, and properly separate concerns (e.g., Validate functions no longer mutate the object being validated)
  • OverlayYAMLData is removed in favor of UnmarshalYAML helper functions and a loaderOptions helper struct that accomplish the same thing
  • our yamlx package is retired/removed
• all documentation updated

[coveralls]

Pull Request Test Coverage Report for Build 19981141368

Details

• 743 of 1845 (40.27%) changed or added relevant lines in 76 files are covered.
• 48 unchanged lines in 18 files lost coverage.
• Overall coverage decreased (-3.6%) to 72.742%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
cmd/trickster/main.go	0	1	0.0%
pkg/appinfo/appinfo.go	0	1	0.0%
pkg/daemon/setup/listeners.go	0	1	0.0%
pkg/proxy/engines/httpproxy.go	4	5	80.0%
pkg/backends/alb/mech/nlm/newest_last_modified.go	0	2	0.0%
pkg/backends/alb/mech/rr/round_robin.go	0	2	0.0%
pkg/cache/registry/registry.go	1	3	33.33%
pkg/proxy/handlers/clickhouse/clickhouse.go	0	2	0.0%
pkg/proxy/handlers/influxdb/influxdb.go	0	2	0.0%
pkg/proxy/handlers/prometheus/prometheus.go	0	2	0.0%

Files with Coverage Reduction	New Missed Lines	%
pkg/backends/alb/mech/ur/user_router.go	1	0.0%
pkg/config/loader.go	1	80.95%
pkg/daemon/setup/setup.go	1	0.0%
pkg/observability/metrics/metrics.go	1	0.0%
pkg/observability/tracing/options/options.go	1	46.6%
pkg/testutil/timeseries/model/model.go	1	0.0%
pkg/observability/tracing/exporters/otlp/otlp.go	2	76.19%
pkg/observability/tracing/exporters/stdout/stdout.go	2	92.73%
pkg/observability/tracing/exporters/zipkin/zipkin.go	2	94.44%
pkg/proxy/engines/proxy_request.go	2	93.42%

Totals
Change from base Build 19951914389:	-3.6%
Covered Lines:	15163
Relevant Lines:	20845

---

💛 - Coveralls

[crandles]

worth adding a constant for this? and perhaps "fgr"?

[crandles]

nit: this seems to be repeated in many tests, you could implement this as

Suggested change

	found := false
	for _, pathConfig := range rsc.BackendOptions.Paths {
	if pathConfig.Path == "/" {
	found = true
	break
	}
	}
	if !found {
	if slices.ContainsFunc([]*po.Options(rsc.BackendOptions.Paths), func(pathConfig *po.Options) bool {
	return pathConfig.Path == "/"
	}) {

[jranson]

Swapped this pattern across all of pkg to use slices.Contains or slices.ContainsFunc instead.