Update the display for sidebar navigation to include section names

[sunithabeeram]

Update the sidebar display as shown in the screenshot. Main change required was to update index.rst to have the :caption: keyword. However, with the referenced sphinx theme, the display of highlevel sections (for ex, "Introduction" in the sidebar) was in a light color (not quite readable). Following the instructions on https://sphinx-rtd-theme.readthedocs.io/en/latest/installing.html, I downloaded the theme and included it in the docs folder and that has made it work better.

[mcvsubbu]

dont know how to review this, but if you can pls create an issue that "View on Gitgub button" is missing, we can add that at a later date.

[sunithabeeram]

@mcvsubbu it looks like the local build isn't displaying the Edit on Github link. Will create an issue if it still is an issue on the main rtd link.

[snleee]

As we discussed offline, we should do the following:

1. remove license check for _themes
2. remove apache license header for external code (css, html, js..etc) and keep them the same as the original code.
3. update LICENSE file

[sunithabeeram]

@snleee updated.

[snleee]

It seems that copying sphinx_rtd_theme pulls another transitive dependencies of some other external js/css/font files. Those need to be handled separately for LICENSE. I think that we can deal with this before cutting a next apache release. For now, let's add sphinx_rtd_theme to LICENSE file.

We can also consider to keep only image & rst files within the source code and come up with some build script that downloads the required js/css/html files (or themes). That will be much cleaner and simpler.

[snleee]

I think that it has to be more specific docs/_themes/sphinx_rtd_theme/* and put its license as LICENSE-sphinx_rtd_theme.txt since sphinx project is different from sphinx_rtd_theme project

[sunithabeeram]

@snleee I've removed the includes for now based on our discussion. Locally, the sphinx-build version I have is v1.6.3. Its perhaps an older one and its possible that the one thats on rtd is newer (I also saw other differences). Will push this code and build it out to ensure things work correctly.

[sunithabeeram]

readthedocs build uses sphinx v1.7.9 and that renders the captions correctly.

[codecov-io]

Codecov Report

Merging #3910 into master will decrease coverage by 25.71%.
The diff coverage is n/a.

@@              Coverage Diff              @@
##             master    #3910       +/-   ##
=============================================
- Coverage     67.13%   41.41%   -25.72%     
=============================================
  Files          1032     1155      +123     
  Lines         50884    57812     +6928     
  Branches       7108     8015      +907     
=============================================
- Hits          34161    23943    -10218     
- Misses        14391    31837    +17446     
+ Partials       2332     2032      -300

Impacted Files	Coverage Δ	Complexity Δ
...inot/core/data/readers/GenericRowRecordReader.java	0% <0%> (-100%)	0% <0%> (ø)
.../org/apache/pinot/common/http/MultiGetRequest.java	0% <0%> (-100%)	0% <0%> (ø)
...n/function/PercentileEstMVAggregationFunction.java	0% <0%> (-100%)	0% <0%> (ø)
...che/pinot/common/restlet/resources/TablesList.java	0% <0%> (-100%)	0% <0%> (ø)
...che/pinot/pql/parsers/pql2/ast/OptionsAstNode.java	0% <0%> (-100%)	0% <0%> (ø)
...ers/pql2/ast/PredicateParenthesisGroupAstNode.java	0% <0%> (-100%)	0% <0%> (ø)
...ot/core/query/scheduler/TableBasedGroupMapper.java	0% <0%> (-100%)	0% <0%> (ø)
...t/core/segment/index/readers/OnHeapDictionary.java	0% <0%> (-100%)	0% <0%> (ø)
...ommon/utils/retry/RetriableOperationException.java	0% <0%> (-100%)	0% <0%> (ø)
...t/core/query/scheduler/OutOfCapacityException.java	0% <0%> (-100%)	0% <0%> (ø)
... and 641 more

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