[7.17] Change elasticsearch.username: elastic deprecation level to critical

[jportner]

Resolves #122704.

This changes the warning in the upgrade assistant:

Testing

Kibana normally forbids you from using this config when running from source.
First, temporarily remove that validation:

diff --git a/src/core/server/elasticsearch/elasticsearch_config.ts b/src/core/server/elasticsearch/elasticsearch_config.ts
index 96b3bdcad1d..5f47092f95e 100644
--- a/src/core/server/elasticsearch/elasticsearch_config.ts
+++ b/src/core/server/elasticsearch/elasticsearch_config.ts
@@ -41,6 +41,7 @@ export const configSchema = schema.object({
       false,
       schema.string({
         validate: (rawConfig) => {
+          return; // don't throw an error here when running from source
           if (rawConfig === 'elastic') {
             return (
               'value of "elastic" is forbidden. This is a superuser account that can obfuscate ' +

Then, add this config to your kibana.yml:

elasticsearch.username: elastic
elasticsearch.password: changeme

Start Elasticsearch and Kibana, log into Kibana, and navigate to the upgrade assistant. You should see the critical deprecation there.

The upgrade assistant is at this route: http://localhost:5601/app/management/stack/upgrade_assistant/kibana_deprecations

8.1 companion PR: #122722 (will be backported to 8.0)

[kibana-ci]

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✅ unchanged

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

[thomheymann]

LGTM!