Define and standardize OSSEC Alert Key terminology

[eloquence]

Similar to freedomofpress/securedrop#4122, let's standardize how we describe the keypair used for OSSEC alerts, and describe this in the glossary. For example, we sometimes call it "the GPG key that OSSEC will encrypt alerts to", but in the installation guide we also refer to it as "the admin’s GPG public key file (for encrypting OSSEC alerts)". Repeating the same long definition over and over again risks introducing small inconsistencies like that.

I would recommend that we call it the OSSEC Alert Key or OSSEC Alert Public Key, and that we call the key for the 24h alerts the Journalist Alert Key or Journalist Alert Public Key (use the most precise qualifier -- public or private -- where possible).

[eloquence]

A recent support ticket shows that the phrase "the admin's GPG public key file" in the docs is definitely causing confusion.

[eloquence]

@joaedwar Good candidate issue for you to work on, will require some searching throughout the docs to identify all ambiguous uses. Happy to clarify as needed.