fix: construct a TraceContext with the correct traceparent

[dk-lockdown]

ref: #50

Ⅰ. Describe what this PR did

Get the full trace of distributed transaction execution

Ⅱ. Does this pull request fix one issue?

Ⅲ. Why don't you add test cases (unit test/integration test)?

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[codecov-commenter]

Codecov Report

Merging #203 (7a39aaf) into dev (d703959) will increase coverage by 0.02%.
The diff coverage is 25.56%.

❗ Current head 7a39aaf differs from pull request most recent head fd5136a. Consider uploading reports for the commit fd5136a to get more accurate results

@@            Coverage Diff             @@
##              dev     #203      +/-   ##
==========================================
+ Coverage   42.80%   42.83%   +0.02%     
==========================================
  Files          81       81              
  Lines        9554     9552       -2     
==========================================
+ Hits         4090     4092       +2     
+ Misses       5058     5054       -4     
  Partials      406      406              

Impacted Files	Coverage Δ
pkg/executor/sharding.go	0.00% <0.00%> (ø)
pkg/filter/dt/exec/prepare_delete.go	46.29% <0.00%> (ø)
pkg/filter/dt/exec/prepare_insert.go	30.76% <0.00%> (ø)
pkg/filter/dt/exec/prepare_update.go	51.08% <0.00%> (ø)
pkg/filter/dt/exec/query_delete.go	51.06% <0.00%> (ø)
pkg/filter/dt/exec/query_insert.go	28.72% <0.00%> (ø)
pkg/filter/dt/exec/query_update.go	53.84% <0.00%> (ø)
pkg/filter/dt/filter_http.go	15.74% <0.00%> (ø)
pkg/filter/dt/filter_mysql.go	1.58% <0.00%> (ø)
pkg/filter/dt/filter_mysql_prepare.go	0.00% <0.00%> (ø)
... and 6 more

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[bohehe]

LGTM