Update instructions for using OSC52 with tmux (#3597)

- **PR Description**
Update the instructions on using copyToClipboardCmd config to copy using
OSC52 with tmux

Added `-w 0` flag to `base64` command because it wraps lines that are
longer than 76 by default, [that fails to copy on some terminal
emulators](#3595).

We compare `$TERM` to `^(screen|tmux)` because both of them are valid as
[per the manual](https://man7.org/linux/man-pages/man1/tmux.1.html):
```
default-terminal terminal
               Set the default terminal for new windows created in this
               session - the default value of the TERM environment
               variable.  For to work correctly, this must be set to
               ‘screen’, ‘tmux’ or a derivative of them.
```

- **Please check if the PR fulfills these requirements**

* [x] Cheatsheets are up-to-date (run `go generate ./...`) -- not
relevant
* [x] Code has been formatted (see
[here](https://github.com/jesseduffield/lazygit/blob/master/CONTRIBUTING.md#code-formatting))
-- not relevant
* [x] Tests have been added/updated (see
[here](https://github.com/jesseduffield/lazygit/blob/master/pkg/integration/README.md)
for the integration test guide) -- not relevant
* [x] Text is internationalised (see
[here](https://github.com/jesseduffield/lazygit/blob/master/CONTRIBUTING.md#internationalisation))
-- not relevant
* [x] Docs have been updated if necessary
* [x] You've read through your own file changes for silly mistakes etc

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docs/Config.md

@@ -667,9 +667,26 @@ os:
 Specify an external command to invoke when copying to clipboard is requested. `{{text}` will be replaced by text to be copied. Default is to copy to system clipboard.
 
 If you are working on a terminal that supports OSC52, the following command will let you take advantage of it:
+```yaml
+os:
+  copyToClipboardCmd: printf "\033]52;c;$(printf {{text}} | base64 -w 0)\a" > /dev/tty
+```
+
+For tmux you need to wrap it with the [tmux escape sequence](https://github.com/tmux/tmux/wiki/FAQ#what-is-the-passthrough-escape-sequence-and-how-do-i-use-it), and enable passthrough in tmux config with `set -g allow-passthrough on`:
+```yaml
+os:
+  copyToClipboardCmd: printf "\033Ptmux;\033\033]52;c;$(printf {{text}} | base64 -w 0)\a\033\\" > /dev/tty
 ```
+
+For the best of both worlds, we can let the command determine if we are running in a tmux session and send the correct sequence:
+```yaml
 os:
-  copyToClipboardCmd: printf "\033]52;c;$(printf {{text}} | base64)\a" > /dev/tty
+  copyToClipboardCmd: >
+    if [[ "$TERM" =~ ^(screen|tmux) ]]; then
+      printf "\033Ptmux;\033\033]52;c;$(printf {{text}} | base64 -w 0)\a\033\\" > /dev/tty
+    else
+      printf "\033]52;c;$(printf {{text}} | base64 -w 0)\a" > /dev/tty
+    fi
 ```
 
 A custom command for reading from the clipboard can be set using