Repo initialisation subcommand creates an index.yaml with a wrong Content-Type

[denismaggior8]

When initialising a new chart repo the plugin creates the initial index.yaml file with a wrong Content-Type metadata attribute.

$ helm gcs init gs://bucket/path
$ gsutil ls -L gs://bucket/path
gs://bucket/path/index.yaml:
    Creation time:          Tue, 20 Jul 2021 00:00:08 GMT
    Update time:            Tue, 20 Jul 2021 00:00:08 GMT
    Storage class:          STANDARD
    Cache-Control:          no-cache, max-age=0, no-transform
    Content-Length:         73
    Content-Type:           text/plain; charset=utf-8
    Hash (crc32c):          heU+XQ==
    Hash (md5):             nS8RrwZ+mwH4lY4OjrqUqg==
    ETag:                   CMP0veWr8PECEAE=
    Generation:             1626739208845891
    Metageneration:         1
    ACL:                    []
TOTAL: 1 objects, 73 bytes (73 B)

The index.yaml Content-Type metadata attribute should be text/yaml or text/x-yaml (according to https://helm.sh/docs/topics/chart_repository/) instead of text/plain.