Add e2e test for proxy baggage-based metadata discovery + fixes

[krinkinmu]

What this PR does / why we need it:

This adds an e2e test for new proxy filters that verifies both baggage
propagation as well as metrics that stats filter will generate.

I also made some changes to how we parse and generate baggage header.
Basically, WorkloadMetadataObject supports cases where app and service
might have different values. In xDS-based metadata discovery
implementation however app is always derived from the service name, at
least in ztunnel.

So there is a bit of a mismatch there. In practice this mismatch should
not matter, but purely hypothetically, if I didn't change the logic, we
could end up in a situation where waypoint node metadata is configured
in such a way that app is set, but service is not. And if that happens,
waypoint will generate a baggage, that ztunnels cannot interpret
correctly yet and it will result in metrics with unknown values.

I figured that I can rewrite code in a way that accounts for all corner
cases like that by making sure that:

1. When we parse baggage we set both app and service, and if any of
   those is not provided in the baggage, we use the other to backfill
2. When we generate baggage, we always generate service (because ztunnel
   needs it), and we generate app, if it's different from the service.

All-in-all, under normal circumstances in the baggage we will only have
service; if app is different from the service - we will add it to the
baggage as well; and when parsing baggage we will use either service or
app, depending on what is provided.

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #

Special notes for your reviewer:

+cc @keithmattix @Stevenjin8 @grnmeira

[krinkinmu]

/retest

[krinkinmu]

/retest

[keithmattix]

@krinkinmu Can you make this PR into master?

[krinkinmu]

/retest-required

[keithmattix]

/retest

[keithmattix]

/retest

[keithmattix]

Can come after branch cut if necessary; it's mostly just a test addition

[keithmattix]

nit: We should note that because we don't use HBONE to the client, there's no source principal (which is expected)

[istio-testing]

In response to a cherrypick label: #6798 failed to apply on top of branch "release-1.29":

Applying: Include myself, Steven and Gustavo as owners of the experimental-ambient-multicluster-telemetry branch (#6772)
Using index info to reconstruct a base tree...
M	CODEOWNERS
Falling back to patching base and 3-way merge...
Auto-merging CODEOWNERS
CONFLICT (content): Merge conflict in CODEOWNERS
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config set advice.mergeConflict false"
Patch failed at 0001 Include myself, Steven and Gustavo as owners of the experimental-ambient-multicluster-telemetry branch (#6772)

[istio-testing]

In response to a cherrypick label: new issue could not be created for failed cherrypick: status code 410 not one of [201], body: {"message":"Issues has been disabled in this repository.","documentation_url":"https://docs.github.com/rest/issues/issues#create-an-issue","status":"410"}