Clear preserved commit message when entering CommitEditorPanel

[ChrisMcD1]

• PR Description

Pretty basic implementation of this fix. The one thing I considered doing that I didn't was to rename OnCommitSuccess, since now 2 out of 4 call sites invoke it prior to make the commit message (and one does it here to invoke a tag, which might be a separate bug)

lazygit/pkg/gui/controllers/helpers/tags_helper.go

Lines 36 to 39 in 5d30409

	return self.gpg.WithGpgHandling(command, git_commands.TagGpgSign, self.c.Tr.CreatingTag, func() error {
	self.commitsHelper.OnCommitSuccess()
	return nil
	}, []types.RefreshableView{types.COMMITS, types.TAGS})

The implementation of OnCommitSuccess also leaves me a bit confused. I'm not sure why it doesn't clear the message every time. By checking with the CommitMessageViewModel.preserveMessage, we only open up the option that we don't clear an existing message should that be false. Is there some world where this is desired? I figure if they are opening the window without the intent to save the message, it would be even more okay to throw away any potential message stored there.

lazygit/pkg/gui/controllers/helpers/commits_helper.go

Lines 160 to 165 in 5d30409

	func (self *CommitsHelper) OnCommitSuccess() {
	// if we have a preserved message we want to clear it on success
	if self.c.Contexts().CommitMessage.GetPreserveMessage() {
	self.c.Contexts().CommitMessage.SetPreservedMessageAndLogError("")
	}
	}

Fixes #4557

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