recorder XKCD 1172: revert fixing gaps, add config param

[j1elo]

What is the current behavior you want to change?

Allow choosing between the original broken behavior or the recorder (keep gaps) and the new one introduced in Kurento 6.15.0 (remove gaps in recordings): https://doc-kurento.readthedocs.io/en/6.15.0/project/relnotes/v6_15_0.html#fixed-recorder-synchronization-on-streaming-gaps

What is the new behavior provided by this change?

• New CONFIG FILE: RecorderEndpoint.conf.ini
• New CONFIG OPTION: gapsFix = (NONE | GENPTS)
• DEFAULT setting: gapsFix=NONE

How has this been tested?

Debug log to show that the feature is enabled. Not really tested yet (will publish experimental packages for it)

Types of changes

• Bug fix (non-breaking change which fixes an issue)

• New feature / enhancement (non-breaking change which improves the project)

• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Kurento 6.15.0 changed the recording behavior because a recording with gaps in it should be considered a bug, thus an invalid file. So the breaking change was allowed within minor versions because it was considered as a bug fix.

But XKCD 1172 came to bite us because we need that the total duration of the recordings matches with the total duration of the sessions that were recorded, which does not happen if you remove timestamp gaps from recordings. So we need to roll back the change.

• My change requires a change to the documentation

Doc changes already included in the PR.

• My change requires a change in other repository

Checklist

• I have read the Contribution Guidelines
• I have added an explanation of what the changes do and why they should be included
• I have written new tests for the changes, as applicable, and have successfully run them locally

Fixes Kurento/bugtracker#570