Lambda searcher: default metastore_uri breaks search

[psanford]

Describe the bug

I'm setting up quickwit in lambda for the first time. I loaded some data with the indexer but when I invoked the search lambda I would get back an index not found error.

After I invoked the searcher I noticed a new file in my s3 bucket that had an unusual looking path:

s3://psanford-quickwit-search/index}#polling_interval=${QW_LAMBDA_SEARCHER_METASTORE_POLLING_INTERVAL_SECONDS:-60s/manifest.json

Note the improperly expanded variable literals.

This appeared to be coming from searcher/environment.rs.

I suspected that this might be related to my issue so I updated the code to:

metastore_uri: s3://${QW_LAMBDA_METASTORE_BUCKET}/index#polling_interval=60s

After deploying this change, the quickwit searcher lambda was able to find my index and return search results.

[rdettai]

The interpolation string looks right, but I also just noticed the error in our internal CI.