Add VictoriaMetrics Database Driver (#376)

[ljluestc]

The implementation supports label filters and time ranges (e.g., victoria://localhost:8428?label_filter={__name__="up"}&start=2020-08-01T00:00:00Z), as requested, and is designed for high-performance data streaming (per VictoriaMetrics’ API docs).

Changes

1. VictoriaMetrics Driver (database/victoria/victoria.go):

   • Added a new driver implementing the database.Driver interface.
   • Supports /api/v1/import for writing time series data (JSON line format).
   • Supports /api/v1/export for reading data with label filters and time ranges.
   • Uses DSN victoria://host:port?label_filter=...&start=...&end=....
   • No version tracking, as VictoriaMetrics is schemaless.

2. Driver Registration (database/database.go):

   • Registered the victoria driver with the database.Register function.

3. Testing (database/victoria/victoria_test.go):

   • Added unit tests for:
     • Importing data via /api/v1/import.
     • Exporting data via /api/v1/export with label filters.
     • Version handling (returns -1, false).
     • Driver closure and error handling.
   • Used a mock HTTP server to simulate VictoriaMetrics APIs.
   • Ran go test ./database/victoria to confirm functionality.

4. Dependencies:

   • Added github.com/VictoriaMetrics/metrics v1.23.0 (optional, for potential metric handling).
   • No other external dependencies.