[FEATURE] logstable: add json export to the logs table

[shahrokni]

Closes perses/perses#3834

Description

This PR adds an export functionality to the logs table by which log entries are flattened and push into an array and can be saved as a JSON file.

The records should already sorted by the timestamp. Therefore, there is no need to sort them at this level.

Every record has the following structure,

export interface LogEntry {
    timestamp: number;
    line: string;
    labels: Labels;
}

Screenshots

Checklist

• Pull request has a descriptive title and context useful to a reviewer.
• Pull request title follows the [<catalog_entry>] <commit message> naming convention using one of the
  following catalog_entry values: FEATURE, ENHANCEMENT, BUGFIX, BREAKINGCHANGE, DOC,IGNORE.
• All commits have DCO signoffs.

UI Changes

• Changes that impact the UI include screenshots and/or screencasts of the relevant changes.
• Code follows the UI guidelines.