feature(layout): add layout config (#866)

feature(layout): add layout config (#866)
* It is now possible to configure zellij through a layout:

  The config file and the layout file will be merged, on conflicting
  options the order is as follows:
  1. config options `zellij options`
  2. layout
  3. config

  Example:
```
---
template:
  direction: Horizontal
  parts:
    - direction: Vertical
      body: true
    - direction: Vertical
      borderless: true
      split_size:
        Fixed: 1
      run:
        plugin:
          location: "zellij:tab-bar"
default_shell: fish
```

1 files changed, 8 insertions, 0 deletions

diff --git a/zellij-utils/src/input/plugins.rs b/zellij-utils/src/input/plugins.rs
index e97a8ad03..6be975e4d 100644
--- a/zellij-utils/src/input/plugins.rs
+++ b/zellij-utils/src/input/plugins.rs
@@ -62,6 +62,14 @@ impl PluginsConfig {
     pub fn iter(&self) -> impl Iterator<Item = &PluginConfig> {
         self.0.values()
     }
+
+    /// Merges two PluginConfig structs into one PluginConfig struct
+    /// `other` overrides the PluginConfig of `self`.
+    pub fn merge(&self, other: Self) -> Self {
+        let mut plugin_config = self.0.clone();
+        plugin_config.extend(other.0);
+        Self(plugin_config)
+    }
 }
 
 impl Default for PluginsConfig {