fix: use tags for codex installation scripts

[drosales57]

Currently the codex installation scripts are installing the latest main commit by default. There's other issues like if the user makes changes to the plugin directory, the git pull will fail because there are uncommitted changes in the directory.

• updated the codex installation scripts to use a variable that holds the release-tag
• the scripts use the release tag value to clone specific release tag branch
• updated README to reference the new command with the tag

other changes to the scripts :

• getting a shallow clone as we don't need to download the whole git history
• backing up the existing plugin directory before cloning to start a clean install
• after cloning, removes the .git folder since we don't need git functionality in the folder

[belluru]

By cleaning the plugin directory, we are removing the existing configs such as database_instance_id etc. but if a user is installing latest version of plugin, the overwrite is bound to happen anyways right? Its probably ok, let me know.

[drosales57]

By cleaning the plugin directory, we are removing the existing configs such as database_instance_id etc. but if a user is installing latest version of plugin, the overwrite is bound to happen anyways right? Its probably ok, let me know.

yea their existing configs would be overwritten regardless if we have to download the plugin repo again

to do things more safely, instead of deleting the the plugin directory, we can rename it so our changes aren't destructive wdyt?
"${INSTALL_DIR}backup$(date +%Y%m%d%H%M%S)"