release v2.1.0-rc.1 (tikv#3514)

* release v2.1.0-rc.1

Signed-off-by: disksing <[email protected]>

*: bump to 2.0.6 (tikv#3392)

*: bump to 2.0.5 (tikv#3288)

raftstore: disable PreVote (tikv#3270)

Release 2.0.4 (tikv#3212)

* Output a log when GC found too many versions for a single key (tikv#3178)

* *: change log for v2.0.4

* *: Bump version.

Bump to 2.0.3 (tikv#3128)

* mysql/decimal: fix a bug in do_div_mod when divisor/dividend is 0  (tikv#3099)

* CHANGELOG: changes for 2.0.2 and 2.0.3 (tikv#3127)

* Bump to 2.0.3

*: bump to 2.0.2 (tikv#3097)

- Support configuring more gRPC related parameters
- Support configuring the timeout range of leader election
- Fix the issue that the Raft log is not printed
- Fix the issue that obsolete learner is not deleted
- Fix the issue that the snapshot intermediate file is mistakenly deleted

Bump to 2.0.1 (tikv#3073)

Merge branch 'master' into release-2.0

Merge branch 'bump-2.0-rc6' into release-2.0