feat(machine-logs): add server side of journal logs (#282)

* Add server side of journal logs

This add the server side and grpc methods to get a journal logs from a
machine. It repurposes ServiceLogEntry for these logs to keep the
changes somewhat to a minimum. And it lets us re-use the merging of the
various logs. In the protobufs ContainerLog has been renamed to just Log
and LogEntry, as these are now also used for journal logs.

It does api.LogOptions in more places to reduce the various logOpts that
were used.

It does not yet plumb it through to the uc client, that needs a follow
up pr. Following logs is also not yet implemented.

Signed-off-by: Miek Gieben <miek@miek.nl>

* Fix test too

Signed-off-by: Miek Gieben <miek@miek.nl>

* remove entire comment

Signed-off-by: Miek Gieben <miek@miek.nl>

* Implement the follow option, untested mind you

Signed-off-by: Miek Gieben <miek@miek.nl>

* update debug line

Signed-off-by: Miek Gieben <miek@miek.nl>

* internal/jounal: First batch of PR comments

Signed-off-by: Miek Gieben <miek@miek.nl>

* internal/journal: code review comments

Signed-off-by: Miek Gieben <miek@miek.nl>

* Manually apply suggestion

Signed-off-by: Miek Gieben <miek@miek.nl>

* apply comment manually

Signed-off-by: Miek Gieben <miek@miek.nl>

* internal/journal: add unit test

Signed-off-by: Miek Gieben <miek@miek.nl>

* Use testify

Signed-off-by: Miek Gieben <miek@miek.nl>

* -amFix scanner.Err checking

Signed-off-by: Miek Gieben <miek@miek.nl>

* Implement code review comments

Signed-off-by: Miek Gieben <miek@miek.nl>

---------

Signed-off-by: Miek Gieben <miek@miek.nl>

internal/machine/api/pb/common.proto

@@ -6,6 +6,7 @@ option go_package = "github.com/psviderski/uncloud/internal/machine/api/pb";
 
 // Vendored at internal/machine/api/vendor/google/rpc/status.proto.
 import "google/rpc/status.proto";
+import "google/protobuf/timestamp.proto";
 
 // Common metadata message nested in all reply message types, injected by the gRPC proxy to provide information
 // about the machine that responded to the request.
@@ -42,3 +43,25 @@ message IPPrefix {
   IP ip = 1;
   uint32 bits = 2;
 }
+
+message LogsRequest {
+  string id = 1;
+  // Options for logs retrieval.
+  bool follow = 2;
+  int32 tail = 3; // -1 means all
+  string since = 4; // https://www.rfc-editor.org/rfc/rfc3339.html timestamp or Go duration string
+  string until = 5; // https://www.rfc-editor.org/rfc/rfc3339.html timestamp or Go duration string
+}
+
+message LogEntry {
+  enum StreamType {
+    UNKNOWN = 0;
+    STDOUT = 1;
+    STDERR = 2;
+    HEARTBEAT = 3;
+  }
+  StreamType stream = 1;
+  google.protobuf.Timestamp timestamp = 2;
+  // Log line content. Empty for heartbeat entries.
+  bytes message = 3;
+}