New Filters: PCR and N-Sigma

[ThibaudCartegnie]

:sparkles: New Filters: PCR and N-Sigma

:bangbang: Once all the checklist is done you have to:

• stash merge this pull request
• delete the corresponding branch
• close the associated issue

:page_with_curl: Type of change

Please delete options that are not relevant.

New feature: non-breaking change which adds functionality.

:bulb: Related Issue(s)

• None

:black_nib: Description

Adds 2 filters:

• PCR : Producer Consumer Ratio : calculates the PC Ratio of every line sent to the filter
• NSigma : Filters the data which does not fit around the mean, alerts the extreme values

:dart: Test Environments

FreeBSD - Vulture ISO (12.2)

• Redis (6.2.6)
• Boost (1.72.0)
• clang++(10.0.1)
• CMake (3.21.3)
• Python (3.8.11)

Ubuntu (20.04)

• Redis (5.0.7)
• Boost (1.71.0)
• g++ (9.3.0)
• CMake (3.16.3)
• Python (3.8.10)
• Valgrind (3.15.0)

:heavy_check_mark: Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] (If new filter) I have added corresponding page to the documentation
• [x] (If other changes) I have made corresponding changes to the documentation
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes

• [x] :raising_hand: I certify on my honor that all the information provided is true, and I've done all I can to deliver a high-quality code