feat(kumactl) add ECDSA certificate generator support

[jpeach]

Summary

Add kumactl support for generating ECDSA TLS certificates. The default is
still RSA certificates, but adding an easy way to generate a self-signed
ECDSA certificate is useful for testing different TLS configurations.

Full changelog

• Add ECDSA support to the kumactl TLS certificate generator

Issues resolved

N/A

Documentation

N/A

Testing

• Unit tests
• E2E tests
• Manual testing on Universal
• Manual testing on Kubernetes

Backwards compatibility

• Add backport-to-stable label if the code is backwards compatible. Otherwise, list breaking changes.

[codecov-commenter]

Codecov Report

Merging #3093 (b430cfa) into master (7575883) will increase coverage by 0.11%.
The diff coverage is 68.18%.

@@            Coverage Diff             @@
##           master    #3093      +/-   ##
==========================================
+ Coverage   52.24%   52.36%   +0.11%     
==========================================
  Files         920      920              
  Lines       53210    53223      +13     
==========================================
+ Hits        27801    27868      +67     
+ Misses      23191    23128      -63     
- Partials     2218     2227       +9     

Impacted Files	Coverage Δ
...d/install/context/install_control_plane_context.go	100.00% <ø> (ø)
...framework/deployments/externalservice/universal.go	3.75% <0.00%> (ø)
test/framework/setup.go	3.58% <0.00%> (ø)
pkg/tls/cert.go	67.24% <66.66%> (-1.28%)	⬇️
app/kumactl/cmd/generate/generate_certificate.go	66.66% <81.81%> (+2.66%)	⬆️
pkg/core/bootstrap/autoconfig.go	46.42% <100.00%> (ø)
pkg/xds/context/context.go	77.77% <100.00%> (ø)
api/observability/v1/mads.pb.go	35.56% <0.00%> (+1.03%)	⬆️
.../core/resources/apis/system/generated_resources.go	77.72% <0.00%> (+2.07%)	⬆️
pkg/mads/v1/client/client.go	43.75% <0.00%> (+2.50%)	⬆️
... and 10 more

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