Relax regex in draft-release.py

[yurishkuro]

Which problem is this PR solving?

• The script expects changelog header with digits only, but last release was with v prefix (as it was shown in the header template).

Description of the changes

• Relax regex in the script to allow v prefix as well

How was this change tested?

• make draft-release was run to create 2.0.0 release

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.47%. Comparing base (3f752c2) to head (a0e27f0).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6189   +/-   ##
=======================================
  Coverage   96.47%   96.47%           
=======================================
  Files         354      354           
  Lines       20126    20126           
=======================================
  Hits        19417    19417           
  Misses        524      524           
  Partials      185      185           

Flag	Coverage Δ
badger_v1	8.31% <ø> (ø)
badger_v2	1.67% <ø> (ø)
cassandra-4.x-v1	14.39% <ø> (ø)
cassandra-4.x-v2	1.61% <ø> (ø)
cassandra-5.x-v1	14.39% <ø> (ø)
cassandra-5.x-v2	1.61% <ø> (ø)
elasticsearch-6.x-v1	18.59% <ø> (ø)
elasticsearch-7.x-v1	18.68% <ø> (+<0.01%)	⬆️
elasticsearch-8.x-v1	18.85% <ø> (ø)
elasticsearch-8.x-v2	1.66% <ø> (ø)
grpc_v1	9.48% <ø> (ø)
grpc_v2	7.00% <ø> (ø)
kafka-v1	8.88% <ø> (ø)
kafka-v2	1.67% <ø> (ø)
memory_v2	1.67% <ø> (ø)
opensearch-1.x-v1	18.73% <ø> (ø)
opensearch-2.x-v1	18.72% <ø> (-0.01%)	⬇️
opensearch-2.x-v2	1.67% <ø> (ø)
tailsampling-processor	0.46% <ø> (ø)
unittests	95.38% <ø> (ø)

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