feat: add name and last four characters to ApiToken model

[mdtro]

• Add a nullable name column to the ApiToken model to help users identify and give meaningful names to their API tokens.
• Add a last_token_characters column that will contain the last four characters of the API token to help users with identify the token in the UI when the majority of it is obfuscated.
• Include a migration that will backfill existing API tokens and their last_token_characters.

Related to RFC => getsentry/rfcs#32.
And issue: #9600

[github-actions]

This PR has a migration; here is the generated SQL for src/sentry/migrations/0584_apitoken_add_name_and_last_four.py src/sentry/migrations/0585_apitoken_backfill_last_chars.py ()

--
-- MIGRATION NOW PERFORMS OPERATION THAT CANNOT BE WRITTEN AS SQL:
-- Raw Python operation
--

[mdtro]

Now that I'm thinking about this. I'll need to separate this into three different PRs to avoid any weird states.

1. Add the name and last_token_characters columns with a migration.
2. Update the save() method on the ApiToken model to save the appropriate characters in the last_token_characters column.
3. Backfill existing API token last characters with a migration.