Add LibriTTS-R recipe

[ShigekiKarita]

Similar to https://github.com/espnet/espnet/tree/master/egs2/libritts_r/tts1

Here are example waveforms (uttid: dev-clean/2277_149897_000031_000002) generated by HiFiGAN trained for 2.5M steps using LibriTTS(-R) datasets:

using groundtruth filterbank

• LibriTTS: baseline_gt_2277_149897_000031_000002_gen.webm
  taken from a link in README.md
• LibriTTS-R: 2277_149897_000031_000002_gen.webm

using TTS filterbank

• LibriTTS: baseline_2277_149897_000031_000002.webm also uses LibriTTS transformer phoneme-to-mel in https://zenodo.org/record/4409702
• LirbiTTS-R: libritts_r_2277_149897_000031_000002.webm

[ShigekiKarita]

Hi, Sorry for being late. I fixed shellcheck errors in my local env.

[ShigekiKarita]

Sorry for bothering you again but I double-checked this time, this command says nothing with the latest stable shellcheck: find egs/libritts_r -name "*.sh" | grep -v path.sh | while read line; do shellcheck -x --shell=bash -P $(dirname $line) ${line}; done

[kan-bayashi]

Sorry for too late merging. Thanks, Shigeki.