Move codecov upload to its own GHA job

[dbwiddis]

Description

Moves the codecov upload out to its own CI job.

• Since it only requires test task it will run even if integ tests fail
• The current location using the CI image is failing upload due to glibc version, see Bump up GCC version to 13.x or later to support SIMD AVX512 fp16 instructions opensearch-build#5226 (scheduled to be fixed in 2.19.0 but moving it is still a good idea per first bullet)

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[dbwiddis]

info - 2025-01-15 18:21:11,222 -- Found 0 coverage files to report
Error: No coverage reports found. Please make sure you're generating reports successfully.

[peterzhuamazon]

Hi @dbwiddis
opensearch-project/opensearch-build#5226 this has nothing to do with glibc thing.
If you have issues see this :
opensearch-project/opensearch-build#5178

Thanks.

[dbwiddis]

Thanks @peterzhuamazon ! Will follow up.

CC: @dhrubo-os