Docs install dir

[stellarsquall]

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This PR updates these files to recommend installing boundary HCL config files in /etc/boundary.d/:

• website/content/docs/installing/high-availability.mdx
• website/content/docs/installing/no-gen-resources.mdx

In addition to the new directory, these files also add changes to the "all-in-one" installation script to create the /etc/boundary.d/ and set 0755 perms on /etc/boundary.d and /usr/local/bin/boundary, like most vault installations recommend:

• website/content/docs/installing/systemd.mdx
• website/content/docs/getting-started/installing/production.mdx