apps: mv kubernetes-external-secrets and node-perf-dash, update existing, add README

[spiffxp]

Part of umbrella issue #2150

I spiraled around the existing apps migrated (gcsweb, sippy) and moved over two more (kubernetes-exteral-secrets, node-perf-dash)

In sum, I tried to converge on and document a few conventions:

• ensure apps/{app} matches the namespace declared in infra/gcp/namespaces/ensure-namespaces.sh
• ensure apps/{app}/deploy.sh exists and is referenced in apps/{app}/README.md - I opted for a copy pasted script, see below
• ensure apps/{app}/OWNERS has a sig/foo label in it
• ensure apps/{app}/*.yaml k8s resources have appropriate labels: { app: {app} } stanzas
• document these and other intended conventions in apps/README.md
• add known issues to apps/README.md and warning that conventions are subject to change as we iterate
• refresh /README.md to reference apps and link to Reorganize apps running on aaa under /apps #2150

The deploy.sh script:

• The script is copy-pasted to make it clear we could likely reduce down to a single parameterized script
• But I didn't reduce down yet, in case we find there are apps that don't fit this model and need to be customized as one-offs

A nice-to-have I did while I was here: sort the buckets used by gcsweb

[k8s-ci-robot]

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[spiffxp]

/cc @ameukam @dims

[spiffxp]

/assign @thockin
for post-merge FYI

[ameukam]

/lgtm
/hold
Remove hold when ready to deploy.

[jimdaga]

nit: spelling humands

[spiffxp]

Good catch, I'll fix this in a followup

[spiffxp]

Followup PR: #2314

[spiffxp]

/hold cancel