Doc - Update install documentation to Elasticsearch/Kibana 8

[AnaelMobilia]

Hi,

I updated the installation documentation in order to manager Elasticsearch / Kibana 8.x release. This release remove nginx reverse proxy requirements as HTTPS can now be used natively on the free version.

Bests regards, Anael

[codecov[bot]]

Codecov Report

Base: 59.23% // Head: 59.23% // No change to project coverage :thumbsup:

Coverage data is based on head (4a43bce) compared to base (49f9d75). Patch has no changes to coverable lines.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #363 +/- ## ======================================= Coverage 59.23% 59.23% ======================================= Files 10 10 Lines 1332 1332 ======================================= Hits 789 789 Misses 543 543 ``` Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=domainaware). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=domainaware)

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[ykcab]

I'll be very cautious on updating this document for anything 8.x. Have you tested that it works with 8.3.x? Ref: #356

[AnaelMobilia]

@ykcab This issue (#356) look to be only on grafana, not reproductible in kibana.

As I see on your PR #366, you look like having found that grafana conf file need to be updated, so I think there is no need to be "very cautious" on this PR :-)

Bests regards, Anael