Tekton simplify CRON validation

[briangleeson]

Simplify the CRON regex values used for validation in tekton timed trigger resources. The new regex allows all valid CRON characters, and the backend API will handle the more detailed validation requirements of the CRON field

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Relates OR Closes #0000

Output from acceptance testing:

$ make testacc TEST=./ibm/service/cdtektonpipeline TESTARGS='-run=TestAccIBMCdTekton*'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./ibm/service/cdtektonpipeline -v -run=TestAccIBMCdTekton* -timeout 700m
=== RUN   TestAccIBMCdTektonPipelineDefinitionDataSourceBasic
--- PASS: TestAccIBMCdTektonPipelineDefinitionDataSourceBasic (95.92s)
=== RUN   TestAccIBMCdTektonPipelinePropertyDataSourceBasic
--- PASS: TestAccIBMCdTektonPipelinePropertyDataSourceBasic (81.45s)
=== RUN   TestAccIBMCdTektonPipelinePropertyDataSourceAllArgs
--- PASS: TestAccIBMCdTektonPipelinePropertyDataSourceAllArgs (65.70s)
=== RUN   TestAccIBMCdTektonPipelineDataSourceBasic
--- PASS: TestAccIBMCdTektonPipelineDataSourceBasic (85.06s)
=== RUN   TestAccIBMCdTektonPipelineDataSourceAllArgs
--- PASS: TestAccIBMCdTektonPipelineDataSourceAllArgs (83.52s)
=== RUN   TestAccIBMCdTektonPipelineTriggerPropertyDataSourceBasic
--- PASS: TestAccIBMCdTektonPipelineTriggerPropertyDataSourceBasic (69.35s)
=== RUN   TestAccIBMCdTektonPipelineTriggerPropertyDataSourceAllArgs
--- PASS: TestAccIBMCdTektonPipelineTriggerPropertyDataSourceAllArgs (82.82s)
=== RUN   TestAccIBMCdTektonPipelineTriggerDataSourceBasic
--- PASS: TestAccIBMCdTektonPipelineTriggerDataSourceBasic (68.52s)
=== RUN   TestAccIBMCdTektonPipelineTriggerDataSourceAllArgs
--- PASS: TestAccIBMCdTektonPipelineTriggerDataSourceAllArgs (85.49s)
=== RUN   TestAccIBMCdTektonPipelineDefinitionBasic
--- PASS: TestAccIBMCdTektonPipelineDefinitionBasic (71.07s)
=== RUN   TestAccIBMCdTektonPipelinePropertyBasic
--- PASS: TestAccIBMCdTektonPipelinePropertyBasic (77.40s)
=== RUN   TestAccIBMCdTektonPipelinePropertyAllArgs
--- PASS: TestAccIBMCdTektonPipelinePropertyAllArgs (118.18s)
=== RUN   TestAccIBMCdTektonPipelineBasic
--- PASS: TestAccIBMCdTektonPipelineBasic (74.82s)
=== RUN   TestAccIBMCdTektonPipelineAllArgs
--- PASS: TestAccIBMCdTektonPipelineAllArgs (120.00s)
=== RUN   TestAccIBMCdTektonPipelineTriggerPropertyBasic
--- PASS: TestAccIBMCdTektonPipelineTriggerPropertyBasic (82.01s)
=== RUN   TestAccIBMCdTektonPipelineTriggerPropertyAllArgs
--- PASS: TestAccIBMCdTektonPipelineTriggerPropertyAllArgs (137.50s)
=== RUN   TestAccIBMCdTektonPipelineTriggerBasic
--- PASS: TestAccIBMCdTektonPipelineTriggerBasic (114.12s)
=== RUN   TestAccIBMCdTektonPipelineTriggerAllArgs
--- PASS: TestAccIBMCdTektonPipelineTriggerAllArgs (150.03s)

PASS
ok      github.com/IBM-Cloud/terraform-provider-ibm/ibm/service/cdtektonpipeline        1664.553s