option to set number of days of logfiles to keep

[pierresetteskog]

A few questions before you begin:

Is this an issue related to the Serilog core project or one of the sinks or
community projects.
This issue list is intended for Serilog Elasticsearch Sink issues. If this issue relates to another sink or to the code project,
please log on the related repository. Please use Gitter chat and Stack Overflow for discussions and questons.

Does this issue relate to a new feature or an existing bug?

• Bug
• New Feature

What version of Serilog.Sinks.Elasticsearch is affected? Please list the related NuGet package.

What is the target framework and operating system? See target frameworks & net standard matrix.

• netCore 2.0
• netCore 1.0
• 4.7
• 4.6.x
• 4.5.x

Please describe the current behavior?
Old log files needs to be removed

Please describe the expected behavior?
in DurableElasticSearchSink.cs i expect an new option options.BufferFileRetainedCountLimit for how many days to keep the files, todays value is null.
Let me know if I should make a PR even if RollingFileSink is deprecated for FilelSink
_sink = new RollingFileSink(
options.BufferBaseFilename + FileNameSuffix,
_state.DurableFormatter,
options.BufferFileSizeLimitBytes,
options.BufferFileRetainedCountLimit);

If the current behavior is a bug, please provide the steps to reproduce the issue and if possible a minimal demo of the problem

[mivano]

Is this still an active issue or already fixed by the latest changes?