use existing connection multiplexer for redis

[Sonic198]

What this PR does / why we need it:
According to documentation Redis connection should be reused across application.

Which issue(s) this PR fixes:
#1773

Please reference the issue this PR will close:
#[1773]

Does this PR introduce a user-facing change?:
Yes.

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• [ x] Code compiles correctly
• [ x] Created/updated tests
• [ x] Unit tests passing
• [ x] End-to-end tests passing

[codecov-commenter]

Codecov Report

Merging #1776 (915db70) into master (2d8fcdf) will increase coverage by 14.61%.
The diff coverage is 95.83%.

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@@             Coverage Diff             @@
##           master    #1776       +/-   ##
===========================================
+ Coverage   51.94%   66.56%   +14.61%     
===========================================
  Files          24      145      +121     
  Lines         616     3930     +3314     
  Branches       66      390      +324     
===========================================
+ Hits          320     2616     +2296     
- Misses        282     1226      +944     
- Partials       14       88       +74     

Flag	Coverage Δ
Aws.SecretsManager	?
Redis	66.82% <95.83%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/HealthChecks.Redis/RedisHealthCheck.cs	79.71% <91.66%> (ø)
...encyInjection/RedisHealthCheckBuilderExtensions.cs	100.00% <100.00%> (ø)

... and 129 files with indirect coverage changes

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[Sonic198]

Is there any problem with this PR?

[sungam3r]

Just a lack of time for all things. I see all the changes and follow the edits.

[esskar]

This is highly needed.

[rob-baldwin]

LGTM

[Sonic198]

Hi, any additional checks/reviews are needed to get this merged ;)?

[Sonic198]

@sungam3r @rob-baldwin could you guys merge this, please?

[sungam3r]

Will be reviewed soon and published in v7.

[sungam3r]

@Sonic198 Thanks. Sometimes it so happens that review of even simple things is delayed for months. I had a break in the OSS, now I'm starting to return to the support of part of the projects that I abandoned.