38 Migrate output callbacks to hooks

[leonstr]

Migrate local_analytics_before_http_headers() and
local_analytics_before_footer() to hooks to reflect change in Moodle 4.4 (see MDL-81144).

Proposed fix for #38 for review.

[bmbrands]

Awesome! thanks for your input. I will give it a test as soon as possible and merge it if successful

[aspark21]

https://moodledev.io/docs/4.4/apis/core/hooks#example-of-hook-callback-registration

Make sure to handle the during_initial_install case

https://tracker.moodle.org/browse/MDL-83001?focusedId=1108277&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-1108277

[leonstr]

https://moodledev.io/docs/4.4/apis/core/hooks#example-of-hook-callback-registration

Make sure to handle the during_initial_install case

@aspark21 No handling for the install/upgrade case is required for this plugin (as far as I can tell).