feat(file-history): customize the max length of commit subject before truncating

[li6in9muyou]

A line of 72 bytes is sometimes deemed too short. An example config is shown below:

    opts = {
      file_history_panel = {
        max_len_commit_subject = 9999,
        win_config = {
          win_opts = {
            wrap = true,
          },
        },
      },
    },