Allow end user to control badger's memory usage

[Avokadoen]

Is your feature request related to a problem? Please describe.
Currently the gowarcserver's can consume more memory than they should in their host container

Describe the solution you'd like
Badger has an extensive API that should enable a solution where the end user can configure the memory usage on startup using arguments and/or the config file. @maeb has a previous attempt at this which can be found on over at the gowarc repo (link is not permanent, so it might die at some point).

Additional context
A good place to start might be badgers documentation entry on memory usage https://dgraph.io/docs/badger/get-started/#memory-usage

All option fields in badger v2.2007.2:
https://github.com/dgraph-io/badger/blob/d5a25b83fbf4f3f61ff03a9202e36f5b75544426/options.go#L35

// Required options.
Dir      string
ValueDir string

// Usually modified options.
SyncWrites          bool
TableLoadingMode    options.FileLoadingMode
ValueLogLoadingMode options.FileLoadingMode
NumVersionsToKeep   int
ReadOnly            bool
Truncate            bool
Logger              Logger
Compression         options.CompressionType
InMemory            bool

// Fine tuning options.

MaxTableSize        int64
LevelSizeMultiplier int
MaxLevels           int
ValueThreshold      int
NumMemtables        int
// Changing BlockSize across DB runs will not break badger. The block size is
// read from the block index stored at the end of the table.
BlockSize          int
BloomFalsePositive float64
KeepL0InMemory     bool
BlockCacheSize     int64
IndexCacheSize     int64
LoadBloomsOnOpen   bool

NumLevelZeroTables      int
NumLevelZeroTablesStall int

LevelOneSize       int64
ValueLogFileSize   int64
ValueLogMaxEntries uint32

NumCompactors        int
CompactL0OnClose     bool
LogRotatesToFlush    int32
ZSTDCompressionLevel int

// When set, checksum will be validated for each entry read from the value log file.
VerifyValueChecksum bool

// Encryption related options.
EncryptionKey                 []byte        // encryption key
EncryptionKeyRotationDuration time.Duration // key rotation duration

// BypassLockGaurd will bypass the lock guard on badger. Bypassing lock
// guard can cause data corruption if multiple badger instances are using
// the same directory. Use this options with caution.
BypassLockGuard bool

// ChecksumVerificationMode decides when db should verify checksums for SSTable blocks.
ChecksumVerificationMode options.ChecksumVerificationMode

// DetectConflicts determines whether the transactions would be checked for
// conflicts. The transactions can be processed at a higher rate when
// conflict detection is disabled.
DetectConflicts bool

// Transaction start and commit timestamps are managed by end-user.
// This is only useful for databases built on top of Badger (like Dgraph).
// Not recommended for most users.
managedTxns bool

// 4. Flags for testing purposes
// ------------------------------
maxBatchCount int64 // max entries in batch
maxBatchSize  int64 // max batch size in bytes

[Avokadoen]

Related pr #10

[Avokadoen]

Note: version of badger has changed drastically since this issue was filed