This may be a breaking change for users who rely on particular kopia metrics (unlikely):
- introduced blob-level metrics:
* `kopia_blob_download_full_blob_bytes_total`
* `kopia_blob_download_partial_blob_bytes_total`
* `kopia_blob_upload_bytes_total`
* `kopia_blob_storage_latency_ms` - per-method latency distribution
* `kopia_blob_errors_total` - per-method error counter
- updated cache metrics to indicate particular cache
* `kopia_cache_hit_bytes_total{cache="CACHE_TYPE"}`
* `kopia_cache_hit_total{cache="CACHE_TYPE"}`
* `kopia_cache_malformed_total{cache="CACHE_TYPE"}`
* `kopia_cache_miss_total{cache="CACHE_TYPE"}`
* `kopia_cache_miss_errors_total{cache="CACHE_TYPE"}`
* `kopia_cache_miss_bytes_total{cache="CACHE_TYPE"}`
* `kopia_cache_store_errors_total{cache="CACHE_TYPE"}`
where `CACHE_TYPE` is one of `contents`, `metadata` or `index-blobs`
- reorganized and unified content-level metrics:
* `kopia_content_write_bytes_total`
* `kopia_content_write_duration_nanos_total`
* `kopia_content_compression_attempted_bytes_total`
* `kopia_content_compression_attempted_duration_nanos_total`
* `kopia_content_compression_savings_bytes_total`
* `kopia_content_compressible_bytes_total`
* `kopia_content_non_compressible_bytes_total`
* `kopia_content_after_compression_bytes_total`
* `kopia_content_decompressed_bytes_total`
* `kopia_content_decompressed_duration_nanos_total`
* `kopia_content_encrypted_bytes_total`
* `kopia_content_encrypted_duration_nanos_total`
* `kopia_content_hashed_bytes_total`
* `kopia_content_hashed_duration_nanos_total`
* `kopia_content_deduplicated_bytes_total`
* `kopia_content_read_bytes_total`
* `kopia_content_read_duration_nanos_total`
* `kopia_content_decrypted_bytes_total`
* `kopia_content_decrypted_duration_nanos_total`
* `kopia_content_uploaded_bytes_total`
Also introduced `internal/metrics` framework which constructs Prometheus metrics in a uniform way and will allow us to include some of these metrics in telemetry report in future PRs.
* cache: refactored reusable portion of cache into separate package
* repo: plumbed through caching for remote repository clients
* repo: plumb through cache in the unit tests
* cache: ensure we only allow absolute cache paths, fixed cache path resolution for remote repositories
