Upgrade go to 1.16

[KanShiori]

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]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• csuzhangxc

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

The full list of commands accepted by this bot can be found here.

Reviewer can indicate their review by submitting an approval review.
Reviewer can cancel approval by submitting a request changes review.

[codecov-commenter]

Codecov Report

Merging #4706 (4e8aee5) into master (9d80655) will decrease coverage by 2.42%.
The diff coverage is 0.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4706      +/-   ##
==========================================
- Coverage   62.41%   59.99%   -2.43%     
==========================================
  Files         196      175      -21     
  Lines       21781    21908     +127     
==========================================
- Hits        13595    13144     -451     
- Misses       6942     7309     +367     
- Partials     1244     1455     +211     

Flag	Coverage Δ
e2e	59.99% <0.00%> (?)
unittest	?

[liubog2008]

/test pull-e2e-kind-across-kubernetes

[liubog2008]

/test pull-e2e-kind-tikv-scale-simultaneously

[KanShiori]

/test pull-e2e-kind-serial

[KanShiori]

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

[KanShiori]

/test pull-e2e-kind

[KanShiori]

/test pull-e2e-kind

[csuzhangxc]

/test pull-e2e-kind

[KanShiori]

/test pull-e2e-kind

[KanShiori]

/test pull-e2e-kind

[KanShiori]

/test pull-e2e-kind

[KanShiori]

/test pull-e2e-kind

[liubog2008]

/test pull-e2e-kind

[ti-srebot]

cherry pick to release-1.3 in PR #4738