feat(cli): optionally store session token in OS keyring (#20256)

This change implements optional secure storage of the CLI token using the operating system
 keyring for Windows, with groundwork laid for macOS in a future change. Previously, the
 Coder CLI stored authentication tokens in plaintext configuration files, which posed a
 security risk because users' tokens are stored unencrypted and can be easily accessed by
 other processes or users with file system access.

The keyring is opt-in to preserve compatibility with applications (like the JetBrains
Toolbox plugin, VS code plugin, etc). Users can opt into keyring use with a new
`--use-keyring` flag.

The secure storage is platform dependent. Windows Credential Manager API is used on Windows.
The session token continues to be stored in plain text on macOS and Linux. macOS is omitted
for now while we figure out the best path forward for compatibility with apps like Coder Desktop.

https://www.notion.so/coderhq/CLI-Session-Token-in-OS-Keyring-293d579be592808b8b7fd235304e50d5

https://github.com/coder/coder/issues/19403

cli/testdata/coder_--help.golden

@@ -108,6 +108,11 @@ variables or flags.
       --url url, $CODER_URL
           URL to a deployment.
 
+      --use-keyring bool, $CODER_USE_KEYRING
+          Store and retrieve session tokens using the operating system keyring.
+          Currently only supported on Windows. By default, tokens are stored in
+          plain text files.
+
   -v, --verbose bool, $CODER_VERBOSE
           Enable verbose output.
 

cli/testdata/coder_login_--help.golden

@@ -5,6 +5,10 @@ USAGE:
 
   Authenticate with Coder deployment
 
+  By default, the session token is stored in a plain text file. Use the
+  --use-keyring flag or set CODER_USE_KEYRING=true to store the token in the
+  operating system keyring instead.
+
 OPTIONS:
       --first-user-email string, $CODER_FIRST_USER_EMAIL
           Specifies an email address to use if creating the first user for the