Implement searching null values

Closes #425

See merge request memri/pod!282

Fixes memri/pod#425

Add a dedicated status code for plugin key decryption error

See merge request memri/pod!281

Allow creating Edge items via the create_item API

See merge request memri/pod!279

Implement edge deletion api

See merge request memri/pod!277

See `cargo audit`

Clean up Synchronization

See merge request memri/pod!274

trigger docs.memri.io pipeline on push to dev

See merge request memri/pod!273

Fix markdown references (attempt 2)

See merge request !272

Fix markdown references

See merge request memri/pod!271

added docker auth config variable

See merge request memri/pod!270

Update libraries, fix fixable CVEs, ignore two CVEs

See merge request memri/pod!269

The two ignored CVEs, "time" RUSTSEC-2020-0071 and
"chrono" RUSTSEC-2020-0159, are considered too hard/ugly
to fix for the moment.

Remove always pulling latest docker image

See merge request memri/pod!267

Always pulling was proposed and introduced as a way
to ensure that Plugins are always used at their latest version.

However, this does not work if a local Plugin is being developed
that does not yet have a published version at all.

It was decided (by the Memri team) to remove the pulling logic
and instead ask people to always pull the image they need.

Allow specifying returnProperties in the API

See merge request memri/pod!266

added hostname in docker-compose

See merge request !264

Add build profile to version information

See merge request !265