Use fslock to acquire lock when reading/writing the tanzu config file for update

[anujc25]

What this PR does / why we need it

• Use fslock to acquire lock when reading the tanzu config file for update
• This PR implements wrapper functions AcquireTanzuConfigLock and ReleaseTanzuConfigLock using fslock.

Which issue(s) this PR fixes

Fixes #2357

Describe testing done for PR

• Added unit tests to read and updated the configuration file in parallel.
• Verified that the unit test fails without this locking mechanism and it is successful with this change.

Release note

Use fslock to acquire lock when reading/writing the tanzu config file for update

PR Checklist

• Squash the commits into one or a small number of logical commits
  
• Use good commit messages
• Ensure PR contains terms all contributors can understand and links all contributors can access

Additional information

Special notes for your reviewer

[github-actions]

Cluster Generation A/B Results:
https://storage.googleapis.com/tkg-clustergen/2882/20220708205027/clustergen.diff.txt
Author/reviewers:
Please review to verify that the effects on the generated cluster configurations are exactly what the PR intended, and give a thumbs-up if so.

[github-actions]

Cluster Generation A/B Results:
https://storage.googleapis.com/tkg-clustergen/2882/20220708212038/clustergen.diff.txt
Author/reviewers:
Please review to verify that the effects on the generated cluster configurations are exactly what the PR intended, and give a thumbs-up if so.

[github-actions]

Cluster Generation A/B Results:
https://storage.googleapis.com/tkg-clustergen/2882/20220708224933/clustergen.diff.txt
Author/reviewers:
Please review to verify that the effects on the generated cluster configurations are exactly what the PR intended, and give a thumbs-up if so.

[codecov]

Codecov Report

Merging #2882 (838da0d) into main (f033cd2) will decrease coverage by 0.07%.
The diff coverage is 31.85%.

@@            Coverage Diff             @@
##             main    #2882      +/-   ##
==========================================
- Coverage   43.80%   43.73%   -0.08%     
==========================================
  Files         414      415       +1     
  Lines       41297    41436     +139     
==========================================
+ Hits        18090    18120      +30     
- Misses      21512    21613     +101     
- Partials     1695     1703       +8     

Impacted Files	Coverage Δ
pkg/v1/auth/csp/grpc.go	0.00% <0.00%> (ø)
pkg/v1/cli/command/core/config.go	36.46% <0.00%> (-1.43%)	⬇️
pkg/v1/cli/command/core/discovery_source.go	38.34% <0.00%> (-2.80%)	⬇️
pkg/v1/cli/command/core/repo.go	14.28% <0.00%> (-1.69%)	⬇️
pkg/v1/config/clientconfig.go	34.79% <45.45%> (-2.50%)	⬇️
pkg/v1/config/lock.go	64.00% <64.00%> (ø)
pkg/v1/config/discovery.go	74.07% <0.00%> (-16.67%)	⬇️
.../cli/plugin/cluster/get_machinehealthcheck_node.go	9.30% <0.00%> (-1.81%)	⬇️
pkg/v1/tkg/tkgpackageclient/package_update.go	83.57% <0.00%> (-1.43%)	⬇️
... and 9 more

---

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[tenczar]

LGTM

[github-actions]

Cluster Generation A/B Results:
https://storage.googleapis.com/tkg-clustergen/2882/20220712193320/clustergen.diff.txt
Author/reviewers:
Please review to verify that the effects on the generated cluster configurations are exactly what the PR intended, and give a thumbs-up if so.

[github-actions]

Cluster Generation A/B Results:
https://storage.googleapis.com/tkg-clustergen/2882/20220712202725/clustergen.diff.txt
Author/reviewers:
Please review to verify that the effects on the generated cluster configurations are exactly what the PR intended, and give a thumbs-up if so.

[github-actions]

Cluster Generation A/B Results:
https://storage.googleapis.com/tkg-clustergen/2882/20220712205444/clustergen.diff.txt
Author/reviewers:
Please review to verify that the effects on the generated cluster configurations are exactly what the PR intended, and give a thumbs-up if so.

[vuil]

lgtm, thanks for the updates

[rajathagasthya]

Is there a way to do this inside config.GetClientConfig and config.StoreClientConfig functions so the callers don't have to worry about it? If I'm using one of those functions, I would ideally expect it to handle all the locking for me.

[anujc25]

Unfortunately, I don't think it is possible without refactoring how we are calling this functions because these external functions use config.GetClientConfig to get the config, update the config as part of the function and use config.StoreClientConfig to update the config. We would like to have the RW lock for this entire read/write operation.

I am not sure we can reliably add locking mechanism as part of config.GetClientConfig and config.StoreClientConfig individually.

[github-actions]

Cluster Generation A/B Results:
https://storage.googleapis.com/tkg-clustergen/2882/20220713173138/clustergen.diff.txt
Author/reviewers:
Please review to verify that the effects on the generated cluster configurations are exactly what the PR intended, and give a thumbs-up if so.