feat: insert_template_after_cursor option

[Kaiser-Yang]

Related issue

None.

Summary of changes

This option make it possible to bind p to paste after and P to paste before.

For example, I have thoes key mappings:

        map_set({ 'n', 'x' }, '<leader>p', function()
            local plus_reg_content = vim.fn.getreg('+'):gsub('\r', '')
            if not utils.markdown_support_enabled() or #plus_reg_content ~= 0 then
                vim.fn.setreg('+', plus_reg_content, vim.fn.getregtype('+'))
                return '"+p'
            else
                return '<cmd>PasteImage<cr>'
            end
        end, { desc = 'Paste from clipboard or insert image', expr = true })
map_set({ 'n', 'x' }, '<leader>P', function()
    local plus_reg_content = vim.fn.getreg('+'):gsub('\r', '')
    local ok, _ = pcall(require, 'img-clip')
    if not utils.markdown_support_enabled() or #plus_reg_content ~= 0 or not ok then
        vim.fn.setreg('+', plus_reg_content, vim.fn.getregtype('+'))
        utils.feedkeys('"+P', 'n')
    else
        require('img-clip').paste_image({ insert_template_after_cursor = false })
    end
end, { desc = 'Paste from clipboard or insert image' })

Using <leader>p at line 19 (put after line 19, and put cursor at line 20):

Using <leader>P at line 19 (put before line 19, and put cursor at line 19; now line 20 is the original line 19):

[hakonharnes]

Overall looks good. See comments on documentation and tests.

[hakonharnes]

Thanks for contributing!