Update the example to use go-app v9 in place of v6

[filmil]

*issues are now fixed, thanks to the kind folks at https://github.com/maxence-charriere/go-app/issues/853

v9 is very different from v6, apparently.

The following changes were necessary:

• Update the dependency to go-app v9.
• Update the go compiler to 1.20.5, since go-app v9 needs go 1.18+
• This in turn required new rules_go.
• This in turn required updating gazeller, and protobufs.
• Ran bazel run //:buildifier to fix the build files.
• Unified the server and client side binaries for the sample app. v9 seems to not like when the two are separated.
• Moved all static web resources to /web/.... This is a requirement in v9, you can not serve these resources from a different subdirectory.
• Removed one last(?) appearance of protoc string in api.proto, which caused gazelle and go mod tidy to get confused.
• Ran ./third_party/update_go_mods. Most deps got updated to newer versions.
• Ran bazel run //:gazelle
• Migrated some of the v6 API that no longer exists to v9.
• Added an icon. Apparently without it, the app will not start (?!)
• Renamed SearchBar, InstanceTable and Manager component variables to exported, because it now makes a difference for computing the UI updates.
• Fix for a somewhat unusual v9 behavior where a component initialized outside of OnMount or app.RouteFunc actually does not get used in building widgets. Leads to bizarre nil pointer accesses. I added comments that explain where the caveats are.

[filmil]

@grahamjenson the v6->v9 migration issues are fixed, you can now merge if you want.

[filmil]

Any interest in merging this? @grahamjenson

[grahamjenson]

Didn't review very closely. Merged with trust :)