Local examples should use pre-built vtadmin-web

[deepthi]

Feature Description

Right now the local example builds vtadmin-web. This is fine for developers (though it slows startup). However, we package the examples and ship them with the binaries.
We should build vtadmin-web in the release script and package it along with the other binaries. Then the Getting Started guides on the website can be changed to use the package.
Local builds via make already build vtadmin-web, so there's no need to rebuild it when running the example locally either.

Use Case(s)

• Users who download the binaries should not have to run through a build to be able to use vtadmin.
• Reduce time taken to run local example in development env.

[deepthi]

Local builds via make already build vtadmin-web, so there's no need to rebuild it when running the example locally either.

This is not the case right now. make all does not call vtadmin_web_install, it should.

That target also needs refining. It currently reads

vtadmin_web_install:
	cd web/vtadmin && npm install

which means it will leave you in web/vtadmin after running the build.
101_initial_cluster.sh does it better

npm --prefix $web_dir --silent install

[deepthi]

Two examples are affected:

% find . -name vtadmin-up.sh
./local/scripts/vtadmin-up.sh
./region_sharding/scripts/vtadmin-up.sh

[deepthi]

It's not yet clear what the best way to "release" vtadmin-web is. Will need some discussion, so let's defer this out of v15.
For anyone running in k8s, this is not a problem since we do publish a vtadmin docker image.