CI: add simple codecov config

[cce]

Summary

Since the codecov app was enabled, it is showing up in PR status checks. This adds a quick configuration based on https://docs.codecov.com/docs/commit-status that we can refine more later.

Test Plan

Status check should pick up changes.

[winder]

FWIW, this is the configuration we came up with for with Indexer: https://github.com/algorand/indexer/blob/develop/.codecov.yml

[Eric-Warehime]

LGTM
Interested to see the output of the coverage checks. You might want to set the patch check to informational as well unless you want that failure to block reviews since I believe both patch and project are configured to run by default.

[codecov]

Codecov Report

Merging #3997 (269c299) into master (91095fa) will increase coverage by 4.68%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3997      +/-   ##
==========================================
+ Coverage   49.77%   54.46%   +4.68%     
==========================================
  Files         409      390      -19     
  Lines       69157    48500   -20657     
==========================================
- Hits        34426    26415    -8011     
+ Misses      31011    19863   -11148     
+ Partials     3720     2222    -1498     

Impacted Files	Coverage Δ
cmd/algoh/blockWatcher.go	77.77% <0.00%> (-3.18%)	⬇️
ledger/acctupdates.go	68.77% <0.00%> (-0.80%)	⬇️
catchup/service.go	68.88% <0.00%> (-0.75%)	⬇️
crypto/merklearray/msgp_gen.go
daemon/algod/api/spec/v2/msgp_gen.go
data/transactions/msgp_gen.go
data/committee/msgp_gen.go
crypto/merklesignature/msgp_gen.go
ledger/msgp_gen.go
data/bookkeeping/msgp_gen.go
... and 19 more

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[cce]

thanks @Eric-Warehime I added patch: too!