fix: Enable ability to exclude survey from appearing on specific pages when survey is enabled

[jswongF5]

Reviewers

@alankrit8 @brentmcomer

Describe the change(s) made and why

When a Medallia or SurveyMonkey is enabled, there wasn't the ability to exclude specific pages that don't need a survey, like the table of contents.

This PR addresses that issue by allowing users to exclude specific pages via a new html_theme_options called feedback_exclude_pages.

The feedback_exclude_pages variable defaults to ['index.html', 'search.html'] which are the table of contents and the search pages.

An example of how a user would setup their own feedback_exclude_pages is below where they don't want the survey to appear on custom.html:

html_theme_options = {
    'feedback_exclude_pages': ['index.html',
                               'search.html',
                               'custom.html']
 }