lib/teleterm: Remove misleading error log after LocalAgent.GetKey

[ravicious]

When you first login to a cluster in Connect and provide the cluster address, Connect creates a profile file for the cluster in Connect's tsh home. Naturally, at this point there's no keys for the cluster. So when you then submit your login credentials and we call clusters.Storage.fromProfile, LocalAgent.GetKey returns a not found error.

In that case we should just continue, similar to how other places in tsh do this:

teleport/tool/tsh/common/kube.go

Lines 142 to 146 in 2cba82c

	// Try loading existing keys.
	k, err = tc.LocalAgent().GetKey(cluster, client.WithKubeCerts{})
	if err != nil && !trace.IsNotFound(err) {
	return trace.Wrap(err)
	}

Instead, the previous version would log the error as if something bad has happened:

Error log

TSHD INFO [CONN:STOR] Unable to load the keys for cluster teleport-local.dev. error:[
TSHD ERROR REPORT:
TSHD Original Error: *trace.NotFoundError open /Users/rav/Library/Application Support/Electron/tsh/keys/teleport-local.dev/rav-x509.pem: no such file or directory
TSHD Stack Trace:
TSHD 	github.com/gravitational/teleport/lib/client/keystore.go:322 github.com/gravitational/teleport/lib/client.(*FSKeyStore).GetKey
TSHD 	github.com/gravitational/teleport/lib/client/client_store.go:82 github.com/gravitational/teleport/lib/client.(*Store).GetKey
TSHD 	github.com/gravitational/teleport/lib/client/keyagent.go:298 github.com/gravitational/teleport/lib/client.(*LocalKeyAgent).GetKey
TSHD 	github.com/gravitational/teleport/lib/teleterm/clusters/storage.go:218 github.com/gravitational/teleport/lib/teleterm/clusters.(*Storage).fromProfile
TSHD 	github.com/gravitational/teleport/lib/teleterm/clusters/storage.go:66 github.com/gravitational/teleport/lib/teleterm/clusters.(*Storage).GetByURI
TSHD 	github.com/gravitational/teleport/lib/teleterm/clusters/storage.go:82 github.com/gravitational/teleport/lib/teleterm/clusters.(*Storage).GetByResourceURI
TSHD 	github.com/gravitational/teleport/lib/teleterm/daemon/daemon.go:131 github.com/gravitational/teleport/lib/teleterm/daemon.(*Service).ResolveCluster
TSHD 	github.com/gravitational/teleport/lib/teleterm/apiserver/handler/handler_auth.go:27 github.com/gravitational/teleport/lib/teleterm/apiserver/handler.(*Handler).Login
TSHD 	github.com/gravitational/teleport/gen/proto/go/teleport/lib/teleterm/v1/service_grpc.pb.go:1076 github.com/gravitational/teleport/gen/proto/go/teleport/lib/teleterm/v1._TerminalService_Login_Handler.func1
TSHD 	github.com/gravitational/teleport/lib/teleterm/apiserver/middleware.go:36 github.com/gravitational/teleport/lib/teleterm/apiserver.withErrorHandling.func1
TSHD 	github.com/gravitational/teleport/gen/proto/go/teleport/lib/teleterm/v1/service_grpc.pb.go:1078 github.com/gravitational/teleport/gen/proto/go/teleport/lib/teleterm/v1._TerminalService_Login_Handler
TSHD 	google.golang.org/grpc@v1.55.0/server.go:1337 google.golang.org/grpc.(*Server).processUnaryRPC
TSHD 	google.golang.org/grpc@v1.55.0/server.go:1714 google.golang.org/grpc.(*Server).handleStream
TSHD 	google.golang.org/grpc@v1.55.0/server.go:959 google.golang.org/grpc.(*Server).serveStreams.func1.1
TSHD 	runtime/asm_arm64.s:1172 runtime.goexit
TSHD User Message: open /Users/rav/Library/Application Support/Electron/tsh/keys/teleport-local.dev/rav-x509.pem: no such file or directory] clusters/storage.go:220

This was spammed frequently enough in the logs that was plain confusing for users submitting logs for troubleshooting – I've seen at least two instances of that.

This PR makes it so that we just log the fact that the keys were not found, without including the error.

[ravicious]

Thanks for quick reviews!

[public-teleport-github-review-bot]

@ravicious See the table below for backport results.

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