[Fleet] Validate asset files to match patterns from spec

[juliaElastic]

While adding a new asset type tag to kibana assets here #114110, it turned out that there is no validation of asset file patterns according to the spec: https://github.com/elastic/package-spec/blob/1e17043c2cf746e7c0168594e51824c903c00e35/versions/1/kibana/spec.yml#L94

Add a check when installing assets to only include files that match the pattern from the spec.

For example:
pattern: '^{PACKAGE_NAME}-.+.json$'`

Rationale, as @mtojek explained:
I can explain why there is the PACKAGE_NAME prefix. Two different packages install their assets and it may happen that they both refer to the same "magic-asset-1". In this case the first installed one will be overridden with the other one, so we want to prevent it using package name prefixes.

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)