feat:add redis ExistsMany method

[codeErrorSleep]

The current Exists function in go-zero's Redis only supports a single key, whereas go-redis's Exists can query multiple keys.
However, directly altering go-zero's Redis implementation would lead to incompatibility between different versions of the method and would affect the implementation of the Store interface in core/stores/kv/store.go.
To ensure compatibility between versions, a new method named ExistsMany should be added as a transitional solution. A unified upgrade can be planned for a later major version release.
close #3765

// go-zero
// core/stores/redis.go:458
v, err := conn.Exists(ctx, key).Result()

// go-redis
Exists(ctx context.Context, keys ...string) *IntCmd

[kevwan]

I think you can just modify Exists method.

[kevwan]

LGTM.

[codecov]

Codecov Report

Merging #3769 (fec125a) into master (8c2f4c1) will decrease coverage by 0.02%.
The diff coverage is 80.00%.

Additional details and impacted files

Files	Coverage Δ
core/stores/redis/redis.go	98.30% <80.00%> (-0.17%)	⬇️