ci: add stale bot

[daixiang0]

Description

Add stale bot to optimize issues/prs lifestyle.

[CodeMonkeyLeet]

LGTM.

@pkedy this is a direct port of the merged dapr/dapr#3248 PR to components-contrib. It will also require a maintainer to add the pinned issues label for the PR exception rule to be overridden as needed.

[pkedy]

Minor nit re: naming

[daixiang0]

@pkedy done.

[daixiang0]

ping @artursouza @yaron2

[codecov]

Codecov Report

Merging #986 (bc47c4c) into master (80f0110) will increase coverage by 0.20%.
The diff coverage is 50.81%.

@@            Coverage Diff             @@
##           master     #986      +/-   ##
==========================================
+ Coverage   34.03%   34.24%   +0.20%     
==========================================
  Files         133      132       -1     
  Lines       10750    10761      +11     
==========================================
+ Hits         3659     3685      +26     
+ Misses       6710     6691      -19     
- Partials      381      385       +4     

Impacted Files	Coverage Δ
bindings/smtp/smtp.go	47.69% <0.00%> (ø)
pubsub/kafka/kafka.go	19.27% <0.00%> (+0.45%)	⬆️
state/memcached/memcached.go	38.23% <50.00%> (+12.78%)	⬆️
state/cassandra/cassandra.go	25.97% <58.33%> (+2.73%)	⬆️
state/redis/redis.go	43.03% <68.00%> (+4.45%)	⬆️

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