feat(logs): 'uc machine logs' to view logs from systemd services on machines (#283)

* logging: client side

Create internal/logs and put abstracted way service and machine logging in there
This adds the bits to do machine logging of the services.

See #273 and discussion in #158

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

* go mod tidy

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

* fix typo

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

* Hook it up further

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

* Check unit validity server side

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

* Make cli-docs

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

* Add newline to logs

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

* docs

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

* Polish a bit

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

* comment fix

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

* There is no groupid

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

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

website/docs/9-cli-reference/uc_machine.md

@@ -22,6 +22,7 @@ Manage machines in the cluster.
 * [uc](uc.md)	 - A CLI tool for managing Uncloud resources such as machines, services, and volumes.
 * [uc machine add](uc_machine_add.md)	 - Add a remote machine to a cluster.
 * [uc machine init](uc_machine_init.md)	 - Initialise a new cluster with a remote machine as the first member.
+* [uc machine logs](uc_machine_logs.md)	 - View systemd service logs.
 * [uc machine ls](uc_machine_ls.md)	 - List machines in a cluster.
 * [uc machine rename](uc_machine_rename.md)	 - Rename a machine in the cluster.
 * [uc machine rm](uc_machine_rm.md)	 - Remove a machine from a cluster and reset it.