[release-1.22] Refactor build_requests

[istio-testing]

Manual cherrypick required.

#1082 failed to apply on top of branch "release-1.22":

Applying: wip
Using index info to reconstruct a base tree...
M	src/proxy.rs
M	src/proxy/inbound.rs
M	src/proxy/inbound_passthrough.rs
M	src/proxy/outbound.rs
M	src/state.rs
M	src/state/workload.rs
Falling back to patching base and 3-way merge...
Auto-merging src/state/workload.rs
Auto-merging src/state.rs
CONFLICT (content): Merge conflict in src/state.rs
Auto-merging src/proxy/outbound.rs
CONFLICT (content): Merge conflict in src/proxy/outbound.rs
Auto-merging src/proxy/inbound_passthrough.rs
Auto-merging src/proxy/inbound.rs
Auto-merging src/proxy.rs
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
Patch failed at 0001 wip
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".