Add a columnFamily feature for client-go when use rawput in tikv

[joccau]

About current rawKV API interface

• It don't support specified columnFamily to put/get/delete and so on. Only support a default columnFamily to manipulate the TiKV by client-go API.

What I want to do

• Create rawKV client firstly
  client := NewRawKVClient(...args)

• If user do not specify columnFamily, Just put key-value into a default columnFamily.
  client.put(key, value)

• If specify columnFamily for client, user can put key-value into this columnFamily.
  client.SetColumnFamily(cf string)
client.put(key, value)

• If specify columnFamily contained in options, user can put key-value into this columnFamily.
  func(c *client) put(key, value []byte, options... Option)
client.put(key, value, SetColumnFamily(cf))

Why I want to enhance

We are developing the feature about backup/restore stream log currently. It observes the key-value records in TiKV layer during backup, and need to put these key-value records into TiKV by rawKV API in client layer during restore.

So we need put these key-value records stored in different columnFamily(default_cf and write_cf) by the RawKV APIs with columnFamily parameters.

[joccau]

/assign

[joccau]

/enhancement

[zz-jason]

could you ellobrate more about the use case of this feature?

[joccau]

could you ellobrate more about the use case of this feature?

As comments above.