feat(gateway): configure overload_manager based on max memory

[michaelbeaumont]

Summary

As suggested by the Envoy docs

This PR checks both Kubernetes limits (via Downward API) directly as well as cgroup limits if they're available.

Checklist prior to review

• Link to docs PR or issue -- Document production usage of MeshGateway kuma-website#931
• Link to UI issue or PR -- Closes Configure the overload manager for Gateway dataplanes #3305
• Is the issue worked on linked? -- Configure the overload manager for Gateway dataplanes #3305 Send Dataplane host resources in xDS metadata #3304
• Unit Tests --
• E2E Tests -- none
• Manual Universal Tests --
• Manual Kubernetes Tests --
• Do you need to update UPGRADE.md? --
• Does it need to be backported according to the backporting policy? -- no

[codecov-commenter]

Codecov Report

Merging #4694 (1f58672) into master (3926791) will increase coverage by 0.01%.
The diff coverage is 59.30%.

@@            Coverage Diff             @@
##           master    #4694      +/-   ##
==========================================
+ Coverage   46.43%   46.45%   +0.01%     
==========================================
  Files         687      687              
  Lines       46702    46788      +86     
==========================================
+ Hits        21688    21736      +48     
- Misses      23094    23128      +34     
- Partials     1920     1924       +4     

Impacted Files	Coverage Δ
pkg/config/app/kuma-dp/config.go	60.86% <ø> (ø)
...ime/k8s/controllers/gateway_instance_controller.go	0.00% <0.00%> (ø)
...pp/kuma-dp/pkg/dataplane/envoy/remote_bootstrap.go	58.16% <37.14%> (-6.24%)	⬇️
pkg/xds/bootstrap/template_v3.go	96.03% <94.59%> (-0.17%)	⬇️
pkg/xds/bootstrap/generator.go	61.06% <100.00%> (+0.48%)	⬆️
pkg/api-server/server.go	74.68% <0.00%> (-2.08%)	⬇️
pkg/xds/generator/direct_access_proxy_generator.go	89.77% <0.00%> (-1.14%)	⬇️
pkg/core/resources/manager/cache.go	85.71% <0.00%> (ø)
pkg/xds/cache/once/once.go	100.00% <0.00%> (+5.00%)	⬆️
pkg/xds/cache/once/cache.go	87.17% <0.00%> (+5.12%)	⬆️

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[jakubdyszkiewicz]

the approach SGTM. Would it make sense to also add this for all DPPs in the system? Not only for gateway

[jakubdyszkiewicz]

Would it make sense to also add this for all DPPs in the system? Not only for gateway

Ok, I see that was answered in another conversation.

[jakubdyszkiewicz]

nice!