Add a convenience redirect to ecosystems.txt (#1967)

Inspired by a request from Dave Tamasi regarding current ecosystems, I
wanted a quicker, easier way to get to `ecosystems.txt`

Also update documentation to better match current `ecosystems.txt`

("it's complicated" with respect to Python (PSF) and GSD and UVI are not
included at https://osv.dev/list)

docs/data.md

@@ -67,8 +67,10 @@ Between the data served in OSV and the data converted to OSV the following ecosy
 -   AlmaLinux
 -   Alpine
 -   Android
+-   Bitnami
 -   crates.io
 -   Debian GNU/Linux
+-   Git ([including C/C++](https://osv.dev/blog/posts/introducing-broad-c-c++-support/))
 -   GitHub Actions
 -   Go
 -   Haskell
@@ -85,6 +87,7 @@ Between the data served in OSV and the data converted to OSV the following ecosy
 -   R (CRAN and Bioconductor)
 -   Rocky Linux
 -   RubyGems
+-   SwiftURL
 
 ## Data dumps
 

gcp/appengine/frontend_handlers.py

@@ -169,6 +169,11 @@ def docs():
   return redirect('https://google.github.io/osv.dev')
 
 
+@blueprint.route('/ecosystems')
+def ecosystems():
+  return redirect('https://osv-vulnerabilities.storage.googleapis.com/ecosystems.txt')  # pylint: disable=line-too-long
+
+
 _LIST_ARGS = ['q', 'ecosystem', 'page']
 
 
@@ -302,10 +307,10 @@ def add_source_info(bug, response):
   response['source'] = source_repo.link + source_path
   response['source_link'] = response['source']
   if source_repo.human_link:
-    ecosystems = bug.ecosystem
+    bug_ecosystems = bug.ecosystem
     bug_id = bug.id()
     response['human_source_link'] = render_template_string(
-        source_repo.human_link, ECOSYSTEMS=ecosystems, BUG_ID=bug_id)
+        source_repo.human_link, ECOSYSTEMS=bug_ecosystems, BUG_ID=bug_id)
 
 
 def _commit_to_link(repo_url, commit):
@@ -346,8 +351,8 @@ def osv_get_ecosystem_counts_cached():
 def osv_get_ecosystem_counts() -> dict[str, int]:
   """Get count of vulnerabilities per ecosystem."""
   counts = {}
-  ecosystems = osv_get_ecosystems()
-  for ecosystem in ecosystems:
+  ecosystem_names = osv_get_ecosystems()
+  for ecosystem in ecosystem_names:
     if ':' in ecosystem:
       # Count by the base ecosystem index. Otherwise we'll overcount as a
       # single entry may refer to multiple sub-ecosystems.