filemanager: implement a querying Lambda function

[mmalenic]

In order to support #109, another Lambda function should be written which processes API gateway requests for querying the database. Some initial query parameters could be supported, e.g. /objects?key=...&bucket=..., or we could have some sort of filter query parameter, e.g. /objects?filter=bucket:bucket-name.

[mmalenic]

If using a filter parameter, we could take inspiration from something like this: https://google.aip.dev/160.

[reisingerf]

Possible initial query use cases as discussed on Slack:

• find all FASTQs (by suffix for now)
• find all files given a portal run id (or more general a path fragment)

Perhaps even combine queries, e.g.

• find VCF, TSV, JSON files for a given portal run id
• find FASTQs created within a given timeframe
• find FASTQs smaller than 10MB
• list FASTQs in archive