enhance mirror node external database feature

[jeromy-cannon]

During the milestone # 1 deployment when deploying Mirror Node using an external Database to GKE a lot of workarounds were applied. This issue is to close some of the gaps and reduce the amount of scripting required to workaround these gaps.

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1. Rename the flag --custom-mirror-node-database-values-path to --use-external-database. Set the description to: "Set to true if you have an external database to use instead of the database that the Mirror Node Helm chart supplies"
2. When --use-external-database is true write the following to the templated values file: stackgres.enabled: false, postgresql.enabled: false, db.name: mirror_node
3. When --use-external-database is true and the database-seeding-query.sql is written out, show a message to the user: "Please run the following SQL script against the external database to enable Mirror Node to function correctly: ${path.join(constants.SOLO_CACHE_DIR, 'database-seeding-query.sql')}"
4. Add a flag --external-database-host for the user to provide the external database host. If it is set, then write the following to the templated values file: db.host: ${externalDatabaseHost}
5. Add a flag --external-database-owner-username for the user to provide the external database privileged owner username. If it is set, then write the following to the templated values file: db.owner.username: ${username}, importer.db.username: ${username}, grpc.db.username: ${username}, rest.db.username: ${username}, restjava.db.username: ${username}, web3.db.username: ${username}
6. Add a flag --external-database-owner-password for the user to provide the external database privileged owner password. If it is set, then write the following to the templated values file: db.owner.password: ${password}, importer.db.password: ${password}, grpc.db.password: ${password}, rest.db.password: ${password}, restjava.db.password: ${password}, web3.db.password: ${password}
7. Update the "Test Taskfile Commands" workflow scripts to leverage the external database and the flags added to support it
8. Update the Taskfile.helper.yml to be able to leverage environment variables from an examples directory Taskfile.yml to then enable the external database and pass in the values
9. Create a examples/custom-mirror-node-database/Taskfile.yml to provide the necessary environment variables to be used for the updated "Test Taskfile Commands"
10. Update the Taskfile.helper.yml and examples/custom-mirror-node-database/Taskfile.yml to be able to deploy a Postgresql instance to the cluster so that it might be used as the external database for Mirror Node in the "Test Taskfile Commands" workflow