feat: add awsiamrds db auth driver (#12566)

cli/testdata/coder_server_--help.golden

@@ -44,6 +44,9 @@ OPTIONS:
           Separate multiple experiments with commas, or enter '*' to opt-in to
           all available experiments.
 
+      --postgres-auth password|awsiamrds, $CODER_PG_AUTH (default: password)
+          Type of auth to use when connecting to postgres.
+
       --postgres-url string, $CODER_PG_CONNECTION_URL
           URL of a PostgreSQL database. If empty, PostgreSQL binaries will be
           downloaded from Maven (https://repo1.maven.org/maven2) and store all

cli/testdata/coder_server_create-admin-user_--help.golden

@@ -7,6 +7,9 @@ USAGE:
   it to every organization.
 
 OPTIONS:
+      --postgres-connection-auth password|awsiamrds, $CODER_PG_CONNECTION_AUTH (default: password)
+          Type of auth to use when connecting to postgres.
+
       --email string, $CODER_EMAIL
           The email of the new user. If not specified, you will be prompted via
           stdin.

cli/testdata/server-config.yaml.golden

@@ -411,6 +411,9 @@ cacheDir: [cache dir]
 # Controls whether data will be stored in an in-memory database.
 # (default: <unset>, type: bool)
 inMemoryDatabase: false
+# Type of auth to use when connecting to postgres.
+# (default: password, type: enum[password\|awsiamrds])
+pgAuth: password
 # The algorithm to use for generating ssh keys. Accepted values are "ed25519",
 # "ecdsa", or "rsa4096".
 # (default: ed25519, type: string)