Feat(cli): Add field count to Timesketch index information

[jaegeral]

This pull request enhances the Timesketch CLI client by adding the ability to display the number of fields present in each index associated with a sketch. This provides users with valuable information about the structure of their data directly from the command line, improving their workflow when working with Timesketch.

Key changes:

• Calculated the number of fields based on the retrieved mapping data.
• Modified the CLI output for sketch/index information to include the fields.

timesketch --sketch 16 timelines describe 18
Name: 2
Index: dd9b6f91f8a04018a44afcb82d762c8d
Status: ready
Event count: 200
Color: F379E1
Number of fields: 407
Name: 2
Created: 2025-01-31T11:01:28.693660
Datasources:
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	Error:
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[jkppr]

Should we make it transparent that the searchindex can contain more than one timeline and therefore the field number does not represent all fields in the timeline but in the searchindex?

[jkppr]

otherwise, lgtm