Shorten metadata.name of PR benchmark pipeline

[gbanasiak]

Looks like #132941 resulted in silent failure with pipeline not installed.

It fails validation as metadata.name cannot exceed 63 characters:

1 validation error for RRE
metadata.name
  String should match pattern '^[a-z0-9A-Z][a-z0-9A-Z_.-]{0,62}$' [type=string_pattern_mismatch, input_value='buildkite-pipeline-elast...t-performance-benchmark', input_type=str]

After this change validation is successful:

Validated (RRE) Resource buildkite-pipeline-elasticsearch-update-serverless-submodule ✓
Validated (RRE) Resource buildkite-pipeline-elasticsearch-check-serverless-submodule ✓
Validated (RRE) Resource buildkite-pipeline-elasticsearch-periodic ✓
Validated (RRE) Resource buildkite-pipeline-elasticsearch-lucene-snapshot-build ✓
Validated (RRE) Resource buildkite-pipeline-elasticsearch-lucene-snapshot-update-branch ✓
Validated (RRE) Resource buildkite-pipeline-elasticsearch-lucene-snapshot-tests ✓
Validated (RRE) Resource buildkite-pipeline-elasticsearch-ecs-dynamic-template-tests ✓
Validated (RRE) Resource buildkite-pipeline-elasticsearch-periodic-micro-benchmarks ✓
Validated (RRE) Resource buildkite-pipeline-elasticsearch-pull-request-perf-benchmark ✓

[elasticsearchmachine]

Pinging @elastic/es-delivery (Team:Delivery)