shut down VC when no keys

[mehdi-aouadi]

PR Description

Shut down immediately when running a standalone validator (teku vc subcommand) without providing any key sources:

• No local keys path
• No external signer
• Not enabling the key-manager API

Fixed Issue(s)

fixes #8290

Documentation

• I thought about documentation and added the doc-change-required label to this PR if updates are required.

Changelog

• I thought about adding a changelog entry, and added one if I deemed necessary.

[rolfyone]

so i guess just for context, to test... startup a minimal node, then create validator config (min-vc.yaml):

network: "auto"
data-path: min-vc
log-destination: "both"

then run

$TEKU vc --config-file min-vc.yaml

expect: fail

run

$TEKU vc --config-file min-vc.yaml --validator-api-enabled --Xvalidator-api-ssl-enabled=false

expect: starts, keymanager is enabled

run

$TEKU vc --config-file min-vc.yaml --validators-external-signer-url http://localhost:19000

expect: starts, remote signer enabled
even without web3signer active

run

$TEKU vc --config-file min-vc.yaml --validator-api-enabled --Xvalidator-api-ssl-enabled=false \
 --validators-external-signer-url http://localhost:19000

expect: starts

all of this was fine.