Return better error message when email is not specified

[matthew-white]

It looks like /v1/users/reset/initiate will return a 500 error if the request body does not have an email property. It'd be better if Central returned a 400 error with a more informative message.

We saw such a request in a deployment of Central v2023.3.1. As to why the request body didn't have an email property, it looks like the Content-Type header of the request was multipart/form-data, not application/json. The following error was thrown:

InvalidInputError: SQL tag cannot be bound an undefined value.
  File "/usr/odk/node_modules/slonik/dist/src/factories/createSqlTag.js", line 27, col 19, in sql
    throw new errors_1.InvalidInputError('SQL tag cannot be bound an undefined value.');
  File "/usr/odk/lib/util/db.js", line 218, col 12, in equals
    : sql`${sql.identifier(k.split('.'))}=${obj[k]}`;
  File "/usr/odk/lib/model/query/users.js", line 71, col 9, in _getSql
    where ${equals(options.condition)} and actors."deletedAt" is null
  File "/usr/odk/lib/model/query/users.js", line 79, col 12, in <anonymous>
    maybeOne(_getSql(options.withCondition({ email }))).then(map(_unjoin));
  File "/usr/odk/lib/model/container.js", line 30, col 33, in Object.module.<computed> [as getByEmail]
    const result = fn(...args)(container);
  File "/usr/odk/lib/resources/users.js", line 47, col 11, in <anonymous>
    Users.getByEmail(body.email)
  File "/usr/odk/lib/http/endpoint.js", line 159, col 26, in <anonymous>
    .then((context) => resource(localContainer.with({ context }), context, request, response))
  File "/usr/odk/node_modules/slonik/dist/src/factories/createSqlTag.js", in runMicrotasks
  File "node:internal/process/task_queues", line 96, col 5, in processTicksAndRejections
  File "/usr/odk/node_modules/slonik/dist/src/connectionMethods/transaction.js", line 22, col 24, in Object.transaction
    const result = await handler(binders_1.bindTransactionConnection(log, connection, clientConfiguration, connection.connection.slonik. {snip}
  File "/usr/odk/node_modules/slonik/dist/src/factories/createConnection.js", line 97, col 18, in Object.createConnection
    result = await connectionHandler(connectionLog, connection, boundConnection, clientConfiguration);