Provide a flexible and simple mechanism to filter entries from the HAR

[derevnjuk]

Description
It would be useful to have a way to filter recorded entries from the resulting HAR file, as the current options (i.e. cy.recordHar({ /* ... */})) do not provide enough flexibility for certain use cases.

Possible solution
We can add a query parameter that allows the user to filter the recorded entries using a Lucene-like syntax, XPath, or JSONPath. For example:

cy.recordHar({ query: 'url:*example.com/* AND contentLength:[10 TO 100]' });

or

cy.recordHar({ query: `$[?(@.url.includes('example.com') && @.contentLength >= 10 && @.contentLength <= 100)]` });

Alternatively, we can allow specifying the path to the module being used to filter them as follows:

// filter.js
module.exports = request => {
  return /example\.com/.test(request.url) && request.contentLength < 100 && request.contentLength > 10;
}

// in the test
cy.recordHar({
  filter: "path/to/filter.js"
});

Additional context
Cypress is spawning an independent child process that runs a plugin. The test is actually running in the browser. While communicating with each other, Cypress serializes command arguments and passes them to the plugin via WebSocket. Therefore, passing a plain JS function is hardly possible. This feature will give the users more control over the data that is saved and make it more efficient.

[derevnjuk]

@cheapsteak I am pleased to inform you that the feature you have been interested in (#85 (comment)) has been released in version 5.13.0.

[cheapsteak]

Thank you so much!