Environment variable names are not validated in the spawner page

Description of problem:

When adding an environment variable with only digits in the name, the build status freezes, and the notebook controller outputs this error:

1.663845121362662e+09 DEBUG events Warning {"object":

, "reason": "FailedCreate", "message": "Reissued from statefulset/jupyter-nb-lferrnan: create Pod jupyter-nb-lferrnan-0 in StatefulSet jupyter-nb-lferrnan failed error: Pod \"jupyter-nb-lferrnan-0\" is invalid: spec.containers[0].env[2].name: Invalid value: \"1341\": a valid environment variable name must consist of alphabetic characters, digits, '_', '-', or '.', and must not start with a digit (e.g. 'my.env-name', or 'MY_ENV.NAME', or 'MyEnvName1', regex used for validation is '[-._a-zA-Z][-._a-zA-Z0-9]*')"}

We should have validation in the frontend to comply with this value.

Prerequisites (if any, like setup, operators/versions):

Steps to Reproduce

1. Go to the spawner page
2. Create a new env variable
3. Fill it with digits, i.e. 1234
4. Start the notebook, it will freeze and it won't output any error.

Actual results:

notebook spawn will freeze and it won't output any error.

Expected results:

When writing an env variable that starts with a number, have form validation.

Reproducibility (Always/Intermittent/Only Once):

always

Build Details:

Workaround:

Not using env variables that start with digits.

Additional info:

a valid environment variable name must consist of alphabetic characters, digits, '_', '-', or '.', and must not start with a digit (e.g. 'my.env-name', or 'MY_ENV.NAME', or 'MyEnvName1', regex used for validation is '[-._a-zA-Z][-._a-zA-Z0-9]*')

Mirroring https://github.com/opendatahub-io/odh-dashboard/issues/586