Use touch instead of mount to check whether config.json is mounted

[nscuro]

Description

Use touch instead of mount to check whether config.json is mounted. In some containerized environments, the mount command is not available, which caused the previous check to fail.

Additionally, modify the config.json file in place when populating it from environment variables, instead of using a temporary file.

The populated config will be logged by the entrypoint script.

Note
Needs to be backported to the 4.9.x branch.

Addressed Issue

Fixes #60
Closes #511
Fixes #513
Closes #514

Additional Details

Example output:

/docker-entrypoint.sh: Launching /docker-entrypoint.d/30-oidc-configuration.sh
30-oidc-configuration.sh: info: effective config: {"API_BASE_URL":null,"API_WITH_CREDENTIALS":null,"OIDC_ISSUER":"foo","OIDC_CLIENT_ID":"bar","OIDC_SCOPE":"openid profile email","OIDC_FLOW":null,"OIDC_LOGIN_BUTTON_TEXT":"baz"}

Checklist

• I have read and understand the contributing guidelines
• This PR introduces new or alters existing behavior, and I have updated the documentation accordingly