[feature] Tune sqlite pragmas

[tsmethurst]

Description

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This pull request implements sqlite pragma tuning, based on #1247 but using the current config structure (since the other method has trouble reading environment variables for nested config values).

When sqlite is used, then the following pragmas will be used by default:

# String. SQLite journaling mode.
# SQLite only -- unused otherwise.
# See: https://www.sqlite.org/pragma.html#pragma_journal_mode
db-sqlite-journal-mode: "WAL"

# String. SQLite synchronous mode.
# SQLite only -- unused otherwise.
# See: https://www.sqlite.org/pragma.html#pragma_synchronous
db-sqlite-synchronous: "NORMAL"

# Byte size. SQlite cache size.
# SQLite only -- unused otherwise.
# See: https://www.sqlite.org/pragma.html#pragma_cache_size
db-sqlite-cache-size: "64MiB"

The PR also disables cache=shared when not running using an in-memory database. It's kept for in-memory for testing purposes.

I'm testing the PR on goblin.technology currently. It seems mostly ok, but i am getting some locked errors every couple minutes:

Jan 16 13:47:40 goblin.technology gotosocial[505318]: timestamp="16/01/2023 13:47:40.327" func=concurrency.(*WorkerPool).Queue.func1 level=ERROR type=worker.Worker[*media.ProcessingMedia] error="error loading media redacted: database is locked (5) (SQLITE_BUSY)" msg="message processing error"
Jan 16 13:54:02 goblin.technology gotosocial[505318]: timestamp="16/01/2023 13:54:02.676" func=concurrency.(*WorkerPool).Queue.func1 level=ERROR type=worker.Worker[messages.FromFederator] error="unexpected error: GetRemoteStatus: error populating status fields: populateStatusFields: error populating status mentions: populateStatusMentions: error creating mention: database is locked (5) (SQLITE_BUSY)" msg="message processing error"
Jan 16 13:58:19 goblin.technology gotosocial[505318]: timestamp="16/01/2023 13:58:19.197" func=concurrency.(*WorkerPool).Queue.func1 level=ERROR type=worker.Worker[messages.FromFederator] error="unexpected error: GetRemoteStatus: error populating status fields: populateStatusFields: error populating status mentions: populateStatusMentions: error creating mention: database is locked (5) (SQLITE_BUSY)" msg="message processing error"
Jan 16 13:59:38 goblin.technology gotosocial[505318]: timestamp="16/01/2023 13:59:38.835" func=concurrency.(*WorkerPool).Queue.func1 level=ERROR type=worker.Worker[messages.FromFederator] error="unexpected error: GetRemoteStatus: couldn't get status author: database error during dereferencing: GetRemoteAccount: error updating remoteAccount: database is locked (5) (SQLITE_BUSY)" msg="message processing error"

For more info on the above errors, see https://www.sqlite.org/wal.html#sometimes_queries_return_sqlite_busy_in_wal_mode

I believe they're being caused by messages being delivered to more than one account at a time, and running multiple concurrent processes to update the same entry. We will probably need to add some kind of locking here to fix this before merging this PR.... @NyaaaWhatsUpDoc did you also run into this problem when testing, or did it not show on a single-user instance?

closes #1335

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[NyaaaWhatsUpDoc]

regarding the DB locked errors, my solution has been setting the busy_timeout parameter. It accepts values in milliseconds, so I'd have a configuration parameter of type time.Duration that you then divide the value of by time.Millisecond. Then set the pragma with strconv.FormatInt() (uses int64 so no, albeit small, risk of value truncation)