add new @actions/attest package

Signed-off-by: Brian DeHamer <[email protected]>

packages/attest/src/index.ts

@@ -0,0 +1,9 @@
+export {AttestOptions, attest} from './attest'
+export {
+  AttestProvenanceOptions,
+  attestProvenance,
+  buildSLSAProvenancePredicate
+} from './provenance'
+
+export type {SerializedBundle} from '@sigstore/bundle'
+export type {Attestation, Predicate, Subject} from './shared.types'