Docs: use https to download the gpg public key

Closes #8818

docs/reference/setup/repositories.asciidoc

@@ -20,7 +20,7 @@ Download and install the Public Signing Key
 
 [source,sh]
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-wget -qO - http://packages.elasticsearch.org/GPG-KEY-elasticsearch | sudo apt-key add -
+wget -qO - https://packages.elasticsearch.org/GPG-KEY-elasticsearch | sudo apt-key add -
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 Add the following to your /etc/apt/sources.list to enable the repository
@@ -51,7 +51,7 @@ Download and install the Public Signing Key
 
 [source,sh]
 --------------------------------------------------
-rpm --import http://packages.elasticsearch.org/GPG-KEY-elasticsearch
+rpm --import https://packages.elasticsearch.org/GPG-KEY-elasticsearch
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 Add the following in your `/etc/yum.repos.d/` directory