fix(jfrog-oauth): fail when access_token is empty

Add a lifecycle precondition to the coder_script resource that validates
the JFrog access token is not empty. This prevents the module from
silently creating configurations with empty tokens when users haven't
authenticated via external auth.

Changes:
- Add precondition check on data.coder_external_auth.jfrog.access_token
- Replace main.test.ts with jfrog-oauth.tftest.hcl for proper data mocking
- Add comprehensive tests covering all package managers (npm, pypi, go,
  docker, conda, maven) with script content validation
- Tests verify actual generated configuration content, not just resource
  existence

Fixes #72

Author: matifali

registry/coder/modules/jfrog-oauth/README.md

@@ -16,7 +16,7 @@ Install the JF CLI and authenticate package managers with Artifactory using OAut
 module "jfrog" {
   count          = data.coder_workspace.me.start_count
   source         = "registry.coder.com/coder/jfrog-oauth/coder"
-  version        = "1.2.3"
+  version        = "1.2.4"
   agent_id       = coder_agent.main.id
   jfrog_url      = "https://example.jfrog.io"
   username_field = "username" # If you are using GitHub to login to both Coder and Artifactory, use username_field = "username"
@@ -57,7 +57,7 @@ Configure the Python pip package manager to fetch packages from Artifactory whil
 module "jfrog" {
   count          = data.coder_workspace.me.start_count
   source         = "registry.coder.com/coder/jfrog-oauth/coder"
-  version        = "1.2.3"
+  version        = "1.2.4"
   agent_id       = coder_agent.main.id
   jfrog_url      = "https://example.jfrog.io"
   username_field = "email"