Optional EventListener on Chart.to_js_literal

[ByronCook]

Please ignore all the line ending diff's. (I'm guessing it's because I'm on Linux or haven't configured my Git client to ignore it)
The change is on line 512/513 and 602-608

I needed a chart which doesn't require an eventlistener as it's loaded on click using HTMX instead of JS, because I'm using HTMX, the DOMContentLoaded isn't being triggered. Using this change I can have the JS code executed immediately instead. This change also allows you to use any other EventListener by providing it as a string.

def to_js_literal(self,
                      filename = None,
                      encoding = 'utf-8',
                      careful_validation = False,
                      event_listener : str = 'DOMContentLoaded',
                      event_listener_enabled : bool = True) -> Optional[str]:

        if event_listener_enabled:
            if event_listener:
                prefix = """document.addEventListener('""" + event_listener + """', function() {\n"""
            else:
                prefix = """document.addEventListener(function() {\n"""
            suffix = """});"""
            as_str = prefix + as_str + '\n' + suffix
        else:
            as_str = as_str

[hcpchris]

Thanks, @ByronCook ! Definitely appreciate the PR. I'll review it shortly and hopefully merge it in for the next minor release.

[codecov]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (6726e8d) 88.25% compared to head (23ef54c) 88.24%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #131      +/-   ##
===========================================
- Coverage    88.25%   88.24%   -0.01%     
===========================================
  Files          209      209              
  Lines        30472    30475       +3     
  Branches      2434     2436       +2     
===========================================
  Hits         26892    26892              
- Misses        2669     2670       +1     
- Partials       911      913       +2     

Files	Coverage Δ
highcharts_core/chart.py	49.65% <50.00%> (-0.35%)	⬇️

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[hcpchris]

Thanks, @ByronCook ! This PR looks good, and it's a welcome addition to the method! I'm going to merge it into the rc-v.1.6 branch that I'm using for our v.1.6 release. Before we roll v.1.6 out, there are some other things that we'll be merging in, and within this PR itself I'm also going to add some docstring details, but I definitely appreciate you filing this PR with this tweak. Thanks!