Add toggle for default setup in docs

[DevPranjal]

Fixes #2436

Description: Added toggles for default setup in docs to avoid confusion

Check list:

• New tests are added (if a new feature is added)
• New doc strings: description and/or example code are in RST format
• Documentation is updated (if required)

[vfdev-5]

@DevPranjal there is a warning that makes docs build to fail:

/home/runner/work/ignite/ignite/docs/source/defaults.rst: WARNING: document isn't included in any toctree

I haven't that warning when built locally

[DevPranjal]

@DevPranjal there is a warning that makes docs build to fail
I haven't that warning when built locally

I had the warning locally too, but the built docs were displaying fine. After searching, I have added the :orphan: metadata tag on top in defaults.rst

[DevPranjal]

@vfdev-5 I have edited the files as discussed to fix the problems with :orphan: tag.

[vfdev-5]

Thanks a lot @DevPranjal , looks great !
Just a small question and we are good to go

[vfdev-5]

@DevPranjal can you please fetch the latest commit from your fork to your local repository (and thus have 1341dff commit) and make an empty commit with amend (just git commit --amend) and push force to your fork such that we can restart the CI and autopep 8 will have nothing to fix in terms of code formatting. Currently the latest commit does not run doctests. Thanks