Upgrade go to 1.16 (#4706)

[ti-srebot]

cherry-pick #4706 to release-1.3
You can switch your code base to this Pull Request by using git-extras:

# In tidb-operator repo:
git pr https://github.com/pingcap/tidb-operator/pull/4738

After apply modifications, you can push your change to this PR via:

git push git@github.com:ti-srebot/tidb-operator.git pr/4738:release-1.3-89faa4d976e0

---

What problem does this PR solve?

What is changed and how does it work?

Upgrade go versions to 1.16 in all go.mod.

Upgrade go versions to 1.16 in e2e

Code changes

• Has Go code change
• Has CI related scripts change

Tests

• Unit test
• E2E test
• Manual test
• No code

Side effects

• Breaking backward compatibility
• Other side effects:

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation

Release Notes

Please refer to Release Notes Language Style Guide before writing the release note.

[ti-chi-bot]

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[ti-srebot]

@KanShiori you're already a collaborator in bot's repo.

[codecov-commenter]

Codecov Report

Merging #4738 (c39e8c7) into release-1.3 (922e517) will increase coverage by 6.55%.
The diff coverage is n/a.

Additional details and impacted files

@@               Coverage Diff               @@
##           release-1.3    #4738      +/-   ##
===============================================
+ Coverage        62.37%   68.92%   +6.55%     
===============================================
  Files              186      190       +4     
  Lines            20869    23340    +2471     
===============================================
+ Hits             13016    16087    +3071     
+ Misses            6638     6011     -627     
- Partials          1215     1242      +27     

Flag	Coverage Δ
e2e	48.21% <ø> (?)
unittest	62.34% <ø> (-0.03%)	⬇️

[liubog2008]

/test pull-e2e-kind

[liubog2008]

/test pull-e2e-kind-serial

[liubog2008]

/test pull-e2e-kind

[csuzhangxc]

/test pull-e2e-kind

[csuzhangxc]

/test pull-e2e-kind
/test pull-e2e-kind-across-kubernetes

[KanShiori]

/test pull-e2e-kind-serial

[KanShiori]

/test pull-e2e-kind

[KanShiori]

/test pull-e2e-kind

[csuzhangxc]

/test pull-e2e-kind

[csuzhangxc]

/test pull-e2e-kind

[csuzhangxc]

/test pull-e2e-kind

[csuzhangxc]

/test pull-e2e-kind

[csuzhangxc]

/test pull-e2e-kind

[csuzhangxc]

/test pull-e2e-kind