*: use native embed package from Go 1.16

[AstroProfundis]

What problem does this PR solve?

Fix #1150 and is related to #1122

What is changed and how it works?

Use native embed package from Go 1.16 to replace 3rd party packages.

⚠️BREAKING CHANGE:

• After this PR, the minimal Go version required to build tiup and builtin components has bumped from 1.13 to 1.16. Developers, please upgrade your toolchain to go1.16.
• The usage of built binaries (for end users) remains unchanged.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

Code changes

• Has exported function/method change
• Has persistent data change

Side effects

• Breaking backward compatibility

Related changes

• Need to update the documentation

Release notes:

*: Use native "embed" package instead of 3rd party package, fix slow startup of `tiup` command
*: Bump required Go version to 1.16

[codecov-io]

Codecov Report

Merging #1151 (ec8aa45) into master (4544229) will decrease coverage by 17.86%.
The diff coverage is 85.71%.

@@             Coverage Diff             @@
##           master    #1151       +/-   ##
===========================================
- Coverage   53.61%   35.75%   -17.87%     
===========================================
  Files         285      222       -63     
  Lines       20308    16011     -4297     
===========================================
- Hits        10889     5724     -5165     
- Misses       7751     9305     +1554     
+ Partials     1668      982      -686     

Flag	Coverage Δ
cluster	35.75% <85.71%> (-9.39%)	⬇️
dm	?
integrate	35.75% <85.71%> (-12.25%)	⬇️
playground	?
tiup	?
unittest	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/cluster/template/config/alertmanager.go	0.00% <0.00%> (ø)
pkg/cluster/template/scripts/dm_master.go	0.00% <0.00%> (-67.22%)	⬇️
pkg/cluster/template/scripts/dm_worker.go	0.00% <0.00%> (-71.43%)	⬇️
embed/embed.go	100.00% <100.00%> (ø)
pkg/cluster/template/config/blackbox.go	63.63% <100.00%> (ø)
pkg/cluster/template/config/config.go	100.00% <100.00%> (ø)
pkg/cluster/template/config/dashboard.go	57.89% <100.00%> (ø)
pkg/cluster/template/config/datasource.go	63.63% <100.00%> (ø)
pkg/cluster/template/config/grafana.go	75.00% <100.00%> (ø)
pkg/cluster/template/config/prometheus.go	66.15% <100.00%> (-6.16%)	⬇️
... and 204 more

---

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[ti-chi-bot]

[REVIEW NOTIFICATION]

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• 9547

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[lucklove]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: ec8aa45

[ti-chi-bot]

@AstroProfundis: Your PR has out-of-dated, I have automatically updated it for you.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[AstroProfundis]

/merge