Rewrite all corrupted tokens before saving in reset_encrypted_tokens

What does this MR do and why?

Rewrite all corrupted tokens before saving in reset_encrypted_tokens

Changelog: fixed

References

gitlab:doctor:reset_encryption_tokens task fail... (#558408 - closed)

How to set up and validate locally

• Update application_settings with invalid encrypted tokens using rails console

setting = ApplicationSetting.first
setting.update_columns(
runners_registration_token_encrypted: 'aaa',
error_tracking_access_token_encrypted: 'bbb'
)

• Run the rake task

MODEL_NAMES=ApplicationSetting TOKEN_NAMES=runners_registration_token,error_tracking_access_token gitlab-rake gitlab:doctor:reset_encrypted_tokens

• Validate the tokens

setting.reload
# should print the updated token without error
puts setting.runners_registration_token
puts setting.error_tracking_access_token

MR acceptance checklist

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