Add Prepend() for prepending mathcher

[k1LoW]

SSIA.

[github-actions]

Code Metrics Report

	main (3dae733)	#128 (188b415)	+/-
Coverage	83.1%	83.4%	+0.2%
Code to Test Ratio	1:0.3	1:0.3	+0.0

Details

  |                    | main (3dae733) | #128 (188b415) |  +/-  |
  |--------------------|----------------|----------------|-------|
+ | Coverage           |          83.1% |          83.4% | +0.2% |
  |   Files            |              3 |              3 |     0 |
  |   Lines            |            654 |            663 |    +9 |
+ |   Covered          |            544 |            553 |    +9 |
+ | Code to Test Ratio |          1:0.3 |          1:0.3 |  +0.0 |
  |   Code             |           2588 |           2443 |  -145 |
  |   Test             |            889 |            889 |     0 |

Code coverage of files in pull request scope (83.6% → 83.9%)

Files	Coverage	+/-
grpcstub.go	83.9%	+0.2%

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Reported by octocov