[FIX] [HEALTH CHECK] Run template and fields checks depends on the app configuration

[Desvelao]

Description

This PR runs the checks related to the alerts index pattern if these are enabled in the app configuration. Add some messages to display when the check is disabled to be skipped or perform some tasks.

The checks when are disabled (value: false in the app configuration):

• checks.pattern: Some actions run.
• checks.template: it is skipped
• checks.fields: it is skipped

When the checks are disabled, it appears a message for each one of them.

Changes

• The check of template and index pattern known fields now depends on the app configuration (checks.template and checks.fields).
• Added messages for when the checks.pattern, checks.template and checks.fields are disabled.
• Fixed typo related to the know fields
• Added checks.fields to the default app configuration file

Tests

• Tests with the next cases deleting all cookies and localstorage data. When a check is disabled, it should display some message about this to skip the check or run some tasks.
  • All checks related to the alerts index pattern enabled:

    checks.pattern: true
    checks.template: true
    checks.fields: true
    

  • Disabled template check:

    checks.pattern: true
    checks.template: false
    checks.fields: true
    

  • Disabled fields check:

    checks.pattern: true
    checks.template: true
    checks.fields: false
    

  • Disabled template and fields checks:

    checks.pattern: true
    checks.template: false
    checks.fields: false
    

  • Disabled all checks:

    checks.pattern: false
    checks.template: false
    checks.fields: false
    

Closes #3765

[asteriscos]

Test: ✔️
CR: ✔️
LGTM