Mercure JWT key does not match symfony/mercure-bundle recipe

[bkosun]

The (default) values of the environment variables MERCURE_JWT_SECRET, MERCURE_PUBLISHER_JWT_KEY, MERCURE_SUBSCRIBER_JWT_KEY do not match the values used in the symfony/mercure-bundle recipe, nor the values specified in the official Symfony documentation:
https://github.com/symfony/recipes/blob/main/symfony/mercure-bundle/0.3/manifest.json
https://github.com/symfony/symfony-docs/pull/17269/files

symfony/recipes#1124

It seems we should use a secret key whose value matches the requirements of lcobucci/jwt ^4.2 to prevent this error:
symfony/mercure#89
lcobucci/jwt#890