Add Rake task for inserting pre-generated access token into database

This task allows inserting a token into the access tokens table without
already having an API token.

To use this, generate a UUID or other random string, and then pass the
hex encoded sha256 digest of that to the `insert` task:

```bash
TOKEN="$(ruby -e "require 'securerandom'; puts SecureRandom.uuid")"
TOKEN_DIGEST="$(ruby -e "require 'digest'; puts Digest::SHA256.hexdigest('$TOKEN')")"

bin/rails access_tokens:insert[$TOKEN_DIGEST]
```

Then don't forget to save the token somewhere safe!

Author: lfdebrux

lib/tasks/access_tokens.rake

@@ -0,0 +1,14 @@
+namespace :access_tokens do
+  desc "Add a pre-generated token, using the SHA256 hex digest"
+  task :insert, %i[token_digest] => :environment do |_, args|
+    usage_message = "usage: rails access_tokens:insert[<token_digest>]".freeze
+    abort usage_message unless args[:token_digest]&.match?(/^[a-f0-9]+$/)
+
+    access_token = AccessToken.create!(
+      description: "inserted with `rails access_tokens:insert`",
+      owner: ENV["USER"],
+      token_digest: args[:token_digest],
+    )
+    pp(access_token)
+  end
+end