Added community projects docs section

[tovbinm]

Related issues
We don't have a dedicated place to keep links to the community projects.

Describe the proposed solution
Added a special docs session to for community projects - https://docs.transmogrif.ai/en/stable/examples/Community-Projects.html (the link wont work until the branch is merged & deployed)

Describe alternatives you've considered
NA

[codecov]

Codecov Report

Merging #326 into master will decrease coverage by 20.23%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master     #326       +/-   ##
===========================================
- Coverage   86.49%   66.26%   -20.24%     
===========================================
  Files         329      329               
  Lines       10599    10599               
  Branches      340      503      +163     
===========================================
- Hits         9168     7023     -2145     
- Misses       1431     3576     +2145

Impacted Files	Coverage Δ
...ala/com/salesforce/op/testkit/InfiniteStream.scala	0% <0%> (-100%)	⬇️
.../scala/com/salesforce/op/test/FeatureAsserts.scala	0% <0%> (-100%)	⬇️
...la/com/salesforce/op/utils/io/avro/AvroInOut.scala	0% <0%> (-100%)	⬇️
...n/scala/com/salesforce/op/readers/CSVReaders.scala	0% <0%> (-100%)	⬇️
.../scala/com/salesforce/op/readers/CSVDefaults.scala	0% <0%> (-100%)	⬇️
...sql/execution/datasources/csv/CSVSchemaUtils.scala	0% <0%> (-100%)	⬇️
...om/salesforce/op/readers/DataFrameFieldNames.scala	0% <0%> (-100%)	⬇️
...alesforce/op/cli/gen/templates/SimpleProject.scala	0% <0%> (-100%)	⬇️
...ala/com/salesforce/op/testkit/RandomIntegral.scala	0% <0%> (-100%)	⬇️
...a/com/salesforce/op/utils/date/DateTimeUtils.scala	0% <0%> (-100%)	⬇️
... and 83 more

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