[Stack Monitoring] Use BasePath.publicBaseUrl for links generated by SM rules

[miltonhultgren]

Based on this SDH: https://github.com/elastic/sdh-kibana/issues/2664

Here is where the rule creates the link URL:

kibana/x-pack/plugins/monitoring/server/alerts/large_shard_size_rule.ts

Lines 171 to 175 in 720fbed

	const globalStateLink = this.createGlobalStateLink(
	`elasticsearch/indices/${shardIndex}`,
	cluster.clusterUuid,
	ccs
	);

We grab the host from these global here:

kibana/x-pack/plugins/monitoring/server/alerts/base_rule.ts

Line 352 in 720fbed

return `${Globals.app.url}/app/monitoring#/${link}?_g=(${globalState.toString()})`;

These globals are defined here, coming from Kibana Core's getServerInfo function:

kibana/x-pack/plugins/monitoring/server/static_globals.ts

Lines 82 to 86 in 720fbed

	const { protocol, hostname, port } = coreSetup.http.getServerInfo();
	const pathname = coreSetup.http.basePath.serverBasePath;
	Globals._app = {
	url: url.format({ protocol, hostname, port, pathname }),

In the docs for getServerInfo it says:

kibana/docs/development/core/server/kibana-plugin-core-server.httpserverinfo.md

Line 7 in 720fbed

Information about what hostname, port, and protocol the server process is running on. Note that this may not match the URL that end-users access Kibana at. For the public URL, see [BasePath.publicBaseUrl](./kibana-plugin-core-server.basepath.publicbaseurl.md)<!-- -->.

We should change this code to make use of BasePath.publicBaseUrl instead.

Affected rules: https://github.com/elastic/kibana/search?q=globalStateLink

[elasticmachine]

Pinging @elastic/infra-monitoring-ui (Team:Infra Monitoring UI)