fix toggleterm & add config for diffview.nvim

[YuCao16]

1. toggleterm.nvim: fix toggleterm start_in_insert not working.
2. diffview.nvim: disable lsp diagnostics in Diffview mode, otherwise, lsp goes crazy due to the conflict markers (<<<) and then crashes.

[ayamir]

1. Can't repro on my wsl.
2. What you introduced is set in the default setup function as diffview.nvim's readme said.

[YuCao16]

1. Can't repro on my wsl.
2. What you introduced is set in the default setup function as diffview.nvim's readme said.

1. Are you using 0.10, because I'm gussing it's a nightly issue for autocmd.

2. I ran into this problem yesterday and I thought it wasn't turned on by default, sorry about this. I will try to create a repro code and raise issue in diffview.

[ayamir]

No, I tested it for 0.9. You should open a pr for 0.10 branch instead of main.

[YuCao16]

No, I tested it for 0.9. You should open a pr for 0.10 branch instead of main.

Sure, I will.