[8.x](backport #43104) feat: add warning log message to indicate vSphere connection is configured as insecure

[mergify]

Proposed commit message

Added a warn log message to all of vSphere metric sets to warn if vSphere connection has been configured as insecure

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.

Disruptive User Impact

Author's Checklist

• [ ]

How to test this PR locally

Related issues

• Closes [vSphere] Warn user if TLS verification is disabled #42986

Use cases

Screenshots

Logs

Example of log entry

{"log.level":"warn","@timestamp":"2025-03-07T11:58:09.323+0200","log.logger":"vsphere.cluster","log.origin":{"function":"github.com/elastic/beats/v7/metricbeat/module/vsphere/security.WarnIfInsecure","file.name":"security/logging.go","file.line":7},"message":"Your vSphere connection is configured as insecure. This can lead to man in the middle attack.","service.name":"metricbeat","metricset":"cluster","ecs.version":"1.6.0"}

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This is an automatic backport of pull request #43104 done by [Mergify](https://mergify.com).