Improve local config list and set handling

[e2e/test_config_local_list_get_set.sh]
- Add a temporary directory and git init to the test script
- Add checks to ensure the output of `gptcommit config list` is valid TOML
- Add checks to ensure the default value is returned when deleting a local configuration setting

Author: zurawiki

e2e/test_config_local_list_get_set.sh

@@ -1,19 +1,26 @@
 #!/bin/sh
 set -eu
 
-gptcommit config list
-# assert is valid TOML
+export TEMPDIR=$(mktemp -d)
+(
+    cd "${TEMPDIR}"
+    git init
 
-gptcommit config get openai.model
-# assert default = text-davinci-003
-gptcommit config set --local openai.model foo
-gptcommit config set openai.model bar
-gptcommit config get openai.model
-# assert is foo
+    gptcommit config list
+    # assert is valid TOML
 
-gptcommit config delete openai.model
-gptcommit config get openai.model
-# assert still is foo
-gptcommit config delete --local openai.model
-gptcommit config get openai.model
-# assert is default
+    gptcommit config get openai.model
+    # assert default = text-davinci-003
+    gptcommit config set --local openai.model foo
+    gptcommit config set openai.model bar
+    gptcommit config get openai.model
+    # assert is foo
+
+    gptcommit config delete openai.model
+    gptcommit config get openai.model
+    # assert still is foo
+    gptcommit config delete --local openai.model
+    gptcommit config get openai.model
+    # assert is default
+)
+rm -rf "${TEMPDIR}"