Support Tensorboard logs dir structure costumizaton
Feature request:
As a user, i would like to have control over checkpoint dir name and structure.
Motivation:
From @janhenriklambrechts (janhenrik.lambrechts@gmail.com):
My logging version directory of a single pytorch-lighting project with tensorboard logs looks something like this:
├── checkpoints
│   ├── epoch=86-max_acc=0.7446.ckpt
│   └── last.ckpt
├── events.out.tfevents.1613393562.lthpc.29645.0
├── hparams.yaml
├── train_acc_classifier_1
│   └── events.out.tfevents.1613393662.lthpc.29645.8
├── train_acc_classifier_2
│   └── events.out.tfevents.1613393662.lthpc.29645.7
├── train_acc_classifier_3
│   └── events.out.tfevents.1613393662.lthpc.29645.6
├── train_acc_classifier_4
│   └── events.out.tfevents.1613393662.lthpc.29645.5
├── val_acc_classifier_1
│   └── events.out.tfevents.1613393563.lthpc.29645.4
├── val_acc_classifier_2
│   └── events.out.tfevents.1613393563.lthpc.29645.3
├── val_acc_classifier_3
│   └── events.out.tfevents.1613393563.lthpc.29645.2
└── val_acc_classifier_4
    └── events.out.tfevents.1613393563.lthpc.29645.1

my network has multiple exits and I thus want to log the val_acc (or train_acc) of all these exits in a single graph which is why I need to log these setups as different runs.
As this is very unorganised and I would want to be able to in one scp -r call get all my tensorboard runs to my laptop.
Therefore I was wondering if there is a way in PL to log not directly in my version_0  folder but in version_0/tb_logs
I would want to be able to tell PL to save my logs in a subfolder tensorboard_logs as such that I only have two folders checkpoints  and tensorboard_logs in this version_0  directory.
I would have assumed that the log_dir  parameter of the TensorboardLogger would be this functionality, however in this case the checkpoints and logs are still together but now in a different main folder.
cc @Borda @tchaton @justusschock @awaelchli @edward-io @ananthsub @rohitgr7 @kamil-kaczmarek @Raalsky @Blaizzy