feat(provisioner): provisioner server implementation

[shanduur]

What this PR does / why we need it:

This pull request addresses several aspects related to the Linode COSI driver for object storage provisioning. The key changes are outlined below:

1. Tests:

   • Added base unit tests for the provisioner.
   • Fixed and extended existing unit tests for improved coverage.
   • Added happy-path integration tests to cover various operations, such as creating a bucket, granting and revoking bucket access, and deleting a bucket.

2. Feature Addition:

   • Added server-side calls to add the complete functionality of the provisioner.

3. Documentation Update:

   • Updated the README to include basic usage information.

4. Example Fixes:

   • Set the correct cluster in the examples for improved clarity.

Which issue(s) this PR resolves:

N/A

Special notes for your reviewer:

The integration tests have prerequisites that need to be met before execution. Ensure the Linode account, API token, and other environment variables are correctly set. Additionally, focus on the newly added server-side calls and verify the correctness of the example fixes.

Additional documentation e.g., enhancement proposals, usage docs, etc.:

Added basic usage documentation located in README.md.

[lgarber-akamai]

Tested locally using the following steps and all OBJ resources seem to have provisioned as expected:

# Build and push the Linode COSI image
docker build -t lgarberakamai/linode-cosi-driver:v0.0.0 --build-arg=VERSION=v0.0.0 --push .

# Install COSI CRDS & controller
kubectl create -k github.com/kubernetes-sigs/container-object-storage-interface-api
kubectl create -k github.com/kubernetes-sigs/container-object-storage-interface-controller

# Install Linode COSI driver
helm upgrade --install linode-cosi ./helm/linode-cosi-driver \
  --set "apiToken=$LINODE_TOKEN" \
  --set "driver.image.repository=docker.io/lgarberakamai/linode-cosi-driver" \
  --set "driver.image.tag=v0.0.0" \
  --namespace linode-cosi-driver --create-namespace

# Apply example manifests
kubectl create -f ./examples
sleep 5

# Validate an OBJ bucket and access keys have been created
linode-cli obj ls
linode-cli object-storage keys-list

# Destroy the example manifests
kubectl destroy -f ./examples
sleep 5

# Validate an OBJ bucket and access keys have been deleted
linode-cli obj ls
linode-cli object-storage keys-list

Great work!