SNOW-1313544 temporal credential cache map race

[sfc-gh-dszmolka]

SNOW-1313544 Parallel operations on different roles cause program to crash (race condition on temporal credential cache) Discovered in a Terraform use-case, where there's a lot of resources handled by the Snowflake Terraform Provider

• moving locks a bit ahead (delete on map happened before lock)
• write-lock instead of read-lock when reading the credentials

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 60.00000% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 75.82%. Comparing base (c165ed5) to head (7c1d8d0).

Files	Patch %	Lines
secure_storage_manager.go	60.00%	4 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1103 +/- ## ========================================== - Coverage 75.83% 75.82% -0.02% ========================================== Files 53 53 Lines 11134 11136 +2 ========================================== Hits 8444 8444 - Misses 2690 2692 +2 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.