Fix Elasticsearch plugin.

[fujiwara]

Hi.

I resolved some problems in mackerel-plugin-elasticsearch.

Support to self-signed cert and basic authorization.

Added -insecure,-user, and -password flags.

Elastcsearch(ES) v8.5 official docker image runs on https with self-signed certificates and requires Basic authentication.

docker run -p 9200:9200 -e "ELASTIC_PASSWORD=pass" -e "discovery.type=single-node" elasticsearch:8.5.0

This command runs the HTTPS server on port 9200, and basic auth 'elastic:pass' is required.

Add -suppress-missing-error flag.

Recent ES versions no longer serve some stats values that are expected by this plugin.

For example, for ES v8.5.0, many errors occurred, as below.

<metrics.plugin.elasticsearch> Failed to find 'filter_cache_size': Cannot handle as a hash
<metrics.plugin.elasticsearch> Failed to find 'evictions_filter_cache': Cannot handle as a hash
<metrics.plugin.elasticsearch> Failed to find 'threads_index': Cannot handle as a hash
<metrics.plugin.elasticsearch> Failed to find 'total_suggest': Cannot handle as a hash
<metrics.plugin.elasticsearch> Failed to find 'threads_suggest': Cannot handle as a hash
<metrics.plugin.elasticsearch> Failed to find 'threads_listener': Cannot handle as a hash
<metrics.plugin.elasticsearch> Failed to find 'threads_snapshot_data': Cannot handle as a hash
<metrics.plugin.elasticsearch> Failed to find 'total_percolate': Cannot handle as a hash
<metrics.plugin.elasticsearch> Failed to find 'threads_bench': Cannot handle as a hash
<metrics.plugin.elasticsearch> Failed to find 'threads_bulk': Cannot handle as a hash
<metrics.plugin.elasticsearch> Failed to find 'threads_optimize': Cannot handle as a hash
<metrics.plugin.elasticsearch> Failed to find 'threads_percolate': Cannot handle as a hash
<metrics.plugin.elasticsearch> Failed to find 'threads_merge': Cannot handle as a hash

These stat values were removed in several versions step by step. (I wrote MISSINGvX comments in codes.)

For backward compatibility, I do not remove these metrics, but I hope to suppress errors.

Added script metrics.

ES has a limitation of script compilation rate.
https://www.elastic.co/guide/en/elasticsearch/reference/current/modules-scripting-using.html

If you compile too many unique scripts within a short time,
Elasticsearch rejects the new dynamic scripts with a circuit_breaking_exception error.

Script metrics help monitor this limitation.

[yseto]

seems good.
Thanks for your contribution.

[yseto]

@fujiwara
We have just released https://github.com/mackerelio/mackerel-agent-plugins/releases/tag/v0.73.0

[fujiwara]

@yseto Thank you!!