[VTAdmin] Remove vtctld web link, improve local example (#15607)

[notfelineit]

This PR is the cherry-pick of #15607

Description

This PR:

• Removes the link to vtctld web, since we deprecated it in v17
• Improves vtadmin-up.sh by 1) outputting the variables that are being set and 2) shortening the wait time for cluster discovery
• Improves web/vtadmin/build.sh by 1) outputting the variables set and 2) when no hostname is set, uses the local machine's hostname

The last bullet point made it so that I could run ./101_initial_clusters.sh without any extra steps, and get vtadmin-web/vtadmin-api working:

[vitess-bot]

Review Checklist

Hello reviewers! 👋 Please follow this checklist when reviewing this Pull Request.

General

• Ensure that the Pull Request has a descriptive title.
• Ensure there is a link to an issue (except for internal cleanup and flaky test fixes), new features should have an RFC that documents use cases and test cases.

Tests

• Bug fixes should have at least one unit or end-to-end test, enhancement and new features should have a sufficient number of tests.

Documentation

• Apply the release notes (needs details) label if users need to know about this change.
• New features should be documented.
• There should be some code comments as to why things are implemented the way they are.
• There should be a comment at the top of each new or modified test to explain what the test does.

New flags

• Is this flag really necessary?
• Flag names must be clear and intuitive, use dashes (-), and have a clear help text.

If a workflow is added or modified:

• Each item in Jobs should be named in order to mark it as required.
• If the workflow needs to be marked as required, the maintainer team must be notified.

Backward compatibility

• Protobuf changes should be wire-compatible.
• Changes to _vt tables and RPCs need to be backward compatible.
• RPC changes should be compatible with vitess-operator
• If a flag is removed, then it should also be removed from vitess-operator and arewefastyet, if used there.
• vtctl command output order should be stable and awk-able.

[deepthi]

Seems like the code owners on this branch is messed up. There is no need for all the people tagged on this PR to be reviewers.