feat: expand supported ecosystems to match Dependabot's full list

[zkoppert]

Problem

Evergreen currently detects 14 package ecosystems, but Dependabot supports 30+. Users with repos using ecosystems we don't detect won't get dependabot configuration suggestions for those ecosystems.

Proposal

Add detection support for the remaining Dependabot-supported ecosystems. Most are straightforward - just adding entries to the package_managers dict in dependabot_file.py.

Easy additions (file-based detection)

Ecosystem	YAML value	Manifest files
Bazel	bazel	MODULE.bazel, WORKSPACE, WORKSPACE.bazel
Bun	bun	bun.lock
Conda	conda	environment.yml, conda.yaml
Docker Compose	docker-compose	docker-compose.yml, compose.yaml
.NET SDK	dotnet-sdk	global.json
Elm	elm	elm.json
Git submodule	gitsubmodule	.gitmodules
Julia	julia	Project.toml
pre-commit	pre-commit	.pre-commit-config.yaml
Pub (Dart)	pub	pubspec.yaml
Rust toolchain	rust-toolchain	rust-toolchain.toml
Swift	swift	Package.swift
uv	uv	uv.lock
vcpkg	vcpkg	vcpkg.json

Medium complexity (directory scanning or special handling)

Ecosystem	YAML value	Notes
Helm	helm	Needs directory scanning for Chart.yaml (similar to terraform)
OpenTofu	opentofu	Shares .tf files with terraform - need to determine how to distinguish or handle overlap

Already covered under existing ecosystems

These use the same YAML values and are already detected by evergreen:

• pipenv / poetry / uv → detected via pip (we already check Pipfile, poetry.lock, pyproject.toml)
• pnpm / yarn → detected via npm (we already check yarn.lock, package-lock.json)

Implementation notes

• Each file-based ecosystem requires ~2 lines in dependabot_file.py (add to package_managers_found dict and package_managers dict)
• Add each new ecosystem to SUPPORTED_PACKAGE_ECOSYSTEMS in env.py
• Add tests in test_dependabot_file.py
• Update README.md EXEMPT_ECOSYSTEMS docs (which is already missing gradle and devcontainers)
• Could be done incrementally (a few ecosystems per PR) or all at once

Additional context

Discovered while working on #489. The current ecosystem list was established in May 2024 and hasn't been expanded since.