Add header input type to support multi headers

[NinaFan0824]

1. Some headers have default values, for example, the assignment rule header is default to true, which we want to update https://developer.salesforce.com/docs/atlas.en-us.api_rest.meta/api_rest/headers_autoassign.htm
2. We also need some headers to make Salesforce Conditional updates Feat/support modification since #5, at the meantime, handle the errors that is likely to be returned when the object doesn't match the conditions. https://developer.salesforce.com/docs/atlas.en-us.api_rest.meta/api_rest/intro_rest_conditional_requests.htm

Currently, ts-force doesn't support adding headers. Based on this, we add some headers to send in patch requests. The below are the headers we intend to add.

Sforce-Auto-Assign: FALSE
If-Match: "Jbjuzw7dbhaEG3fd90kJbx6A0ow=-gzip", "U5iWijwWbQD18jeiXwsqxeGpZQk=-gzip"
If-None-Match: "Jbjuzw7dbhaEG3fd90kJbx6A0ow=-gzip", "U5iWijwWbQD18jeiXwsqxeGpZQk=-gzip"
If-Modified-Since: Tue, 10 Aug 2015 00:00:00 GMT
If-Unmodified-Since: Tue, 10 Aug 2015 00:00:00 GMT
Sforce-Mru: updateMru=true
x-sfdc-packageversion-clientPackage: 1.0 //x-sfdc-packageversion-[namespace]: xx.x , where [namespace] is the unique namespace of the managed package and xx.x is the package version.

[ChuckJonas]

Is Generic-Header just allowing an arbitrary header key/value?

If so, it seems like you would want to potentially support multiple values. It might also be easier to just allow a Record<string, string>.

additionalHeaders?: Record<string, string>;

[ChuckJonas]

Might want to include the header keys in the exception

[ChuckJonas]

I've never actually used these etag caching headers with Salesforce... Reviewing the docs, I see this statement:

An optional header specifying a comma-delimited list of one or more ETags. This only has an effect when used with Account objects. The request is only processed if the Account’s ETag does not match one of the ETags in the list.

Does it really only work with Account?

[NinaFan0824]

From the document here, Etag is used for http caching. I guess that’s the reason why it’s said only work with Account. I test with a a case project, and If-Match and If-None-Match can be added on get request but not on patch request.

[jackholmes1010]

I would recommend undoing the formatting changes

[jackholmes1010]

Is this a breaking change? Should we increment the major version?