Introduce self-healing SSH client with connection management

[fastrapier]

This pull request introduces a new self-healing SSH client implementation in the internal/infrastructure/ssh/v2 package, alongside updates to documentation and dependencies. The new client separates connection strategy from operations, provides transparent reconnection, and is designed for extensibility and robust error handling. No existing consumers have been migrated yet; the legacy SSH client remains in place.

Key changes:

New self-healing SSH client (ssh/v2)

• Added a new package internal/infrastructure/ssh/v2 implementing a self-healing SSH client with a clear separation between connection strategy (via Dialer and Route) and operations (currently tunneling, future support for Run/Upload). The client transparently handles reconnects, deduplicates concurrent reconnects using singleflight, and offers options for keepalive, retries, logging, and host key handling. The core logic is in client.go and conn.go, with a generic executor for reconnect-aware operations. [1] [2]

Documentation updates

• Updated docs/ARCHITECTURE.md to describe the new ssh/v2 package, its design, API, and extension points. The documentation now distinguishes between the legacy SSH client and the new implementation, and details the responsibilities and structure of the new code. [1] [2] [3]
• Added a new entry to docs/WORKLOG.md summarizing the introduction of the self-healing SSH client, its design, API, and test strategy.

Dependency management

• Added golang.org/x/sync as a direct dependency in go.mod to support the use of singleflight for deduplicating concurrent reconnects.

[github-code-quality]

Code Coverage Overview

Languages: Go

Go / code-coverage/go

The overall coverage in the feat/new-ssh-client branch is 5%. The coverage in the main branch is 2%.

Show a code coverage summary of the most impacted files.

File	main 60ef4b8	feat/new-ssh-client 6ad749c	+/-
internal/logger/logger.go	36%	39%	+3%
internal/infras.../v2/endpoint.go	0%	37%	+37%
internal/infras...sh/v2/dialer.go	0%	39%	+39%
internal/infras...h/v2/options.go	0%	53%	+53%
internal/infras...sh/v2/client.go	0%	79%	+79%
internal/infras.../ssh/v2/conn.go	0%	86%	+86%
internal/infras...sh/v2/tunnel.go	0%	87%	+87%
internal/infras...sh/v2/errors.go	0%	100%	+100%

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[github-actions]

Package	Line Rate	Health
github.com/deckhouse/storage-e2e/internal/cluster	0%	❌
github.com/deckhouse/storage-e2e/internal/config	15%	❌
github.com/deckhouse/storage-e2e/internal/infrastructure/ssh	0%	❌
github.com/deckhouse/storage-e2e/internal/infrastructure/ssh/v2	69%	➖
github.com/deckhouse/storage-e2e/internal/kubernetes/commander	0%	❌
github.com/deckhouse/storage-e2e/internal/kubernetes/deckhouse	0%	❌
github.com/deckhouse/storage-e2e/internal/kubernetes/storage	0%	❌
github.com/deckhouse/storage-e2e/internal/kubernetes/virtualization	0%	❌
github.com/deckhouse/storage-e2e/internal/logger	51%	❌
github.com/deckhouse/storage-e2e/internal/provisioning/dvp	7%	❌
github.com/deckhouse/storage-e2e/pkg/cluster	0%	❌
github.com/deckhouse/storage-e2e/pkg/clusterprovider	89%	✔
github.com/deckhouse/storage-e2e/pkg/clusterprovider/registry	100%	✔
github.com/deckhouse/storage-e2e/pkg/kubernetes	0%	❌
github.com/deckhouse/storage-e2e/pkg/retry	0%	❌
github.com/deckhouse/storage-e2e/pkg/storage-e2e	0%	❌
github.com/deckhouse/storage-e2e/pkg/testkit	0%	❌
Summary	5% (625 / 12984)	❌