[BEAM-10961] Make mongo-java-driver dependency a named variable

[shehzaadn-vd]

This PR implements a change suggested in PR# 13830. The mongo_java_driver created here will subsequently be used in that PR.

R: @ibzib

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Post-Commit Tests Status (on master branch)

Lang	SDK	Dataflow	Flink	Samza	Spark	Twister2
Go		---		---		---
Java
Python				---		---
XLang				---		---

Pre-Commit Tests Status (on master branch)

---	Java	Python	Go	Website	Whitespace	Typescript
Non-portable
Portable	---		---	---	---	---

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GitHub Actions Tests Status (on master branch)

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[codecov]

Codecov Report

Merging #13910 (827c938) into master (52d0bd9) will increase coverage by 0.00%.
The diff coverage is n/a.

@@ Coverage Diff @@## master #13910 +/- ##
=======================================
Coverage 82.85% 82.85% =======================================
Files 466 466 Lines 57596 57596 =======================================
+ Hits 47719 47723 +4 + Misses 9877 9873 -4 

Impacted Files	Coverage Δ
sdks/python/apache_beam/io/localfilesystem.py	91.66% <0.00%> (-0.76%)	⬇️
...ks/python/apache_beam/runners/worker/sdk_worker.py	89.54% <0.00%> (-0.16%)	⬇️
setup.py	0.00% <0.00%> (ø)
sdks/python/apache_beam/runners/common.py	88.87% <0.00%> (+0.14%)	⬆️
sdks/python/apache_beam/dataframe/frames.py	90.94% <0.00%> (+0.41%)	⬆️
sdks/python/apache_beam/internal/metrics/metric.py	87.50% <0.00%> (+1.04%)	⬆️

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[shehzaadn-vd]

@ibzib would you be able to review and merge this?

[ibzib]

LGTM