docs: Update deprecated install command (#4409)

* docs: Update deprecated install command

* docs: Update command to add repo

website/content/docs/install-boundary/install.mdx

@@ -46,12 +46,12 @@ binary:
    package-signing key:
 
     ```shell-session
-    $ curl -fsSL https://apt.releases.hashicorp.com/gpg | sudo apt-key add -
+    $ curl -fsSL https://apt.releases.hashicorp.com/gpg | sudo gpg --dearmor -o /usr/share/keyrings/hashicorp-archive-keyring.gpg
     ```
 1. Add the official HashiCorp Linux repository:
 
     ```shell-session
-    $ sudo apt-add-repository "deb [arch=amd64] https://apt.releases.hashicorp.com $(lsb_release -cs) main"
+    $ echo "deb [signed-by=/usr/share/keyrings/hashicorp-archive-keyring.gpg] https://apt.releases.hashicorp.com $(lsb_release -cs) main" | sudo tee /etc/apt/sources.list.d/hashicorp.list
     ```
 
 1. Update the package index:
@@ -121,12 +121,12 @@ binary:
    package-signing key:
 
     ```shell-session
-    $ curl -fsSL https://apt.releases.hashicorp.com/gpg | sudo apt-key add -
+    $ curl -fsSL https://apt.releases.hashicorp.com/gpg | sudo gpg --dearmor -o /usr/share/keyrings/hashicorp-archive-keyring.gpg
     ```
 1. Add the official HashiCorp Linux repository:
 
     ```shell-session
-    $ sudo apt-add-repository "deb [arch=amd64] https://apt.releases.hashicorp.com $(lsb_release -cs) main"
+    $ echo "deb [signed-by=/usr/share/keyrings/hashicorp-archive-keyring.gpg] https://apt.releases.hashicorp.com $(lsb_release -cs) main" | sudo tee /etc/apt/sources.list.d/hashicorp.list
     ```
 
 1. Update the package index: