[BEAM-8185] Properly backup sys config files in release script

[markflyhigh]

Following changes only affects Python mobilegaming varification in run_rc_validation.sh:

• Add timestep to backup file name to make them unique (~/.bashrc and ~/.m2/settings.xml)
• Reorder m2 and bashrc config step. Move them out of python version loop since they are independent to Python version and only need to config once. This can avoid duplicate run which will overwrite backup files.
• Reorder start data injection pipeline. Move it up and outside of python version loop so that all mobile gaming pipelines consume from its output. Originally, the script created one data injector per python version, which is unnecessary.

Manual test from local machine.

+R: @yifanzou @boyuanzz

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Post-Commit Tests Status (on master branch)

Lang	SDK	Apex	Dataflow	Flink	Gearpump	Samza	Spark
Go		---	---		---	---
Java
Python		---			---	---
XLang	---	---	---		---	---	---

Pre-Commit Tests Status (on master branch)

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

See .test-infra/jenkins/README for trigger phrase, status and link of all Jenkins jobs.

[yifanzou]

LGTM

[boyuanzz]

Thanks Mark!