add initial dev maintenance doc

Noticed that Velero does not have a dev maintenance doc. Templated one from Loki and added my Velero testing deployment config.

docs/DEVELOPMENT_MAINTENANCE.md

+# To upgrade the Velero Package
+
+Check the [upstream changelog](url_needed) and the [helm chart upgrade notes](url_needed).
+
+# Upgrading
+
+## Update dependencies  
+  
+To Do
+
+## Update binaries
+
+Pull assets and commit the binaries as well as the Chart.lock file that was generated.
+```
+helm dependency update ./chart
+``` 
+
+## Update chart
+
+```chart/Chart.yaml```
+- To Do
+
+# Modifications made to upstream
+This is a high-level list of modifitations that Big Bang has made to the upstream helm chart. You can use this as as cross-check to make sure that no modifications were lost during the upgrade process.
+
+```chart/values.yaml```
+- To Do
+
+
+# Testing new Velero Version
+
+- Deploy Velero as a part of BigBang  
+```
+helm upgrade \
+  --install bigbang ./bigbang/chart \
+  --create-namespace \
+  --namespace bigbang \
+  --values ./bigbang/chart/values.yaml \
+  --values ./bigbang/chart/ingress-certs.yaml \
+  --values ./overrides/ib_creds.yaml \
+  --values ./overrides/velero.yaml \
+  --values ./overrides/minio.yaml \
+  --set monitoring.enabled=true \
+  --set kyverno.enabled=false \
+  --set kyvernopolicies.enabled=false \
+  --set clusterAuditor.enabled=false \
+  --set gatekeeper.enabled=false \
+  --set twistlock.enabled=false \
+  --set eckoperator.enabled=false \
+  --set fluentbit.enabled=false \
+  --set logging.enabled=false \
+  --set jaeger.enabled=false
+```
+`overrides/velero.yaml`
+```
+addons:
+  velero:
+    enabled: true
+    plugins:
+    - aws
+    values:
+      image:
+        imagePullSecrets:
+        - private-registry
+
+      initContainers: 
+        - name: velero-plugin-for-aws
+          image: registry1.dso.mil/ironbank/opensource/velero/velero-plugin-for-aws:v1.5.0
+          imagePullPolicy: IfNotPresent
+          volumeMounts:
+            - mountPath: /target
+              name: plugins
+          resources:
+            requests:
+              memory: 512Mi
+              cpu: 100m
+            limits:
+              memory: 512Mi
+              cpu: 100m
+
+      configuration:
+        provider: aws
+        backupStorageLocation:
+          bucket: velero99
+          config:
+            region: "us-gov-west-1"
+            insecureSkipTLSVerify: "true"
+            s3ForcePathStyle: "true"
+            s3Url: http://minio.minio.svc
+        volumeSnapshotLocation:
+          provider: aws
+          config:
+            region: "us-gov-west-1"
+
+      credentials:
+        useSecret: true
+        secretContents:
+          cloud: |
+            [default]
+            aws_access_key_id = minio
+            aws_secret_access_key = minio123
+
+      # Set a service account so that the CRD clean up job has proper permissions to delete CRDs
+      serviceAccount:
+        server:
+          name: velero
+
+      cleanUpCRDs: true
+
+      networkPolicies:
+        enabled: true
+
+      bbtests:
+        enabled: true
+```
+`overrides/minio.yaml`
+```
+addons:
+  minioOperator:
+    enabled: true
+
+  minio:
+    enabled: true
+    values:
+      tenants:
+        pools:
+        - servers: 2
+          volumesPerServer: 4
+          size: 256Mi
+          resources:
+            requests:
+              cpu: 250m
+              memory: 2Gi
+            limits:
+              cpu: 250m
+              memory: 2Gi
+          securityContext:
+            runAsUser: 1001
+            runAsGroup: 1001
+            fsGroup: 1001
+            runAsNonRoot: true
+      bbtests:
+        enabled: false
+        cypress:
+          envs:
+            cypress_url: 'https://minio.bigbang.dev/login'
+        scripts:
+          envs:
+            MINIO_PORT: ''
+            MINIO_HOST: 'https://minio-api.bigbang.dev'
+```
+
+- Visit `https://prometheus.bigbang.dev`
+- ...more to do...
+