DEVX-2249: Create centralized custom dictionary for spell checking; fix spelling errors

[ybyzek]

Description

https://confluentinc.atlassian.net/browse/DEVX-2249

What behavior does this PR change, and why?

1. Consistent spell check against validated word list
2. Spelling error in Clickstream demo

Example how to run with the word list:

brew install aspell
for f in $(find . -name "*.rst") ; do aspell list -p ~/git/examples/docs/wordlist.txt < $f ; done  | sort  | uniq

Author Validation

Describe the validation already done, or needs to be done, by the PR submitter.

• Documentation (local build)

• clickstream (@bbejeck -- this PR surfaced an error in the clickstream demo itself! -- it was due to my spelling mistake)

Reviewer Tasks

Describe the tasks/validation that the PR submitter is requesting to be done by the reviewer.

[rspurgeon]

@ybyzek very nice... can you add some instructions on how you used the word list?

[ybyzek]

@ybyzek very nice... can you add some instructions on how you used the word list?

@rspurgeon sure thing, added to Description of this PR and https://confluentinc.atlassian.net/browse/DEVX-2249

[rspurgeon]

LGTM