[Metricbeat] Add a switch to the driver definition on SQL module to use pretty names

[sayden]

What does this PR do?

SQL module directly passes the driver name to the sqlx library. This must match the library name used in Metricbeat: mysql for MySQL, postgresql for PostgreSQL but godror for Oracle which is ugly in terms of UX.

Why is it important?

Docs shouldn't fix UX issues so this PR fixes this in code.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

How to test this PR locally

• Launch Oracle Docker Image

docker run --name oracle -d -p 1521:1521 store/oracle/database-enterprise:12.2.0.1

• Configure SQL module as follows. Metricbeat will need to be configured to use Oracle driver as follows https://www.elastic.co/guide/en/beats/metricbeat/current/metricbeat-module-oracle.html:

# Module: sql
# Docs: https://www.elastic.co/guide/en/beats/metricbeat/7.7/metricbeat-module-sql.html

- module: sql
  metricsets:
    - query
  period: 10s
  hosts: ["oracle://sys:Oradoc_db1@172.17.0.2:1521/ORCLPDB1.localdomain?sysdba=1"]

  driver: "oracle"
  sql_query: "SELECT TABLESPACE_NAME, TABLESPACE_SIZE, ALLOCATED_SPACE, FREE_SPACE FROM DBA_TEMP_FREE_SPACE"
  sql_response_format: table

• An event is generated with the driver name oracle

[elasticmachine]

Pinging @elastic/integrations-services (Team:Services)

[ycombinator]

I like what this PR is trying to do, which is to hide the implementation (the driver library name) from the interface (the pretty name). This also gives us the option of swapping out a driver library for another one while not requiring any changes from users.

The way this PR is currently implemented, however, a user would be able to specify either oracle or godror as the pretty name. Is this what we want? Or should we keep a map[string][string] of pretty names => implementation driver library names and error out if the pretty name key isn't found in the map?

[sayden]

I thought about doing a map but then if we add a new SQL-based module (ie Clickhouse) we'll need to update the map (which is going to be out of the context of the "other sql module" PR).

The alternative is to use a map to names we know which are "ugly" only like godror but leave the possibility to use any "unknown" pretty name. WDYT?

[ycombinator]

Fair point, @sayden. Let's keep this as-is then — the user can specify the "pretty" name for the godror module or the actual name of the driver itself.

[ycombinator]

LGTM. WFG.