Kibana: [SR] Snapshot name forced to lowercase

[sw-jung]

Kibana version: 7.4.1

Elasticsearch version: 7.4.1

Original install method (e.g. download page, yum, from source, etc.):

# docker-compose.yml
version: '2'
services:
  elasticsearch:
    image: docker.elastic.co/elasticsearch/elasticsearch:7.4.1
    container_name: elasticsearch
    environment:
      - discovery.type=single-node
      - bootstrap.memory_lock=true
      - path.repo=/usr/share/elasticsearch/snapshot
      - ES_JAVA_OPTS=-Xms512m -Xmx512m
    ulimits:
      memlock:
        soft: -1
        hard: -1
    ports:
      - '9200:9200'
    volumes:
      - '.\data:/usr/share/elasticsearch/data'
      - '.\snapshot:/usr/share/elasticsearch/snapshot'
  kibana:
    image: docker.elastic.co/kibana/kibana:7.4.1
    container_name: kibana
    ports:
      - '5601:5601'

Describe the bug: When creating a new snapshot policy on Kibana, snapshot name forced to lowercase even if it containing date math.

Steps to reproduce:

1. Go to create a new snapshot policy
2. Enter <snapshot-{now/d{yyyy.MM.dd|+09:00}}> in the snapshot name
3. Go next

Expected behavior: Snapshot name can be lowercase, but some of date math (e.g. M) needs uppercase.

Screenshots (if relevant):

[elasticmachine]

Pinging @elastic/es-ui (Team:Elasticsearch UI)

[lucabelluccini]

Just to add a comment: the SLM API works correctly (the date math is not lower-cased).

[turnUpTheChill]

++