Rename pulsar lambda parameter due to name clash

Description

In the PulsarParameters structure (and deprecated BinaryPulsarParameters structure) a variable called LAMBDA is currently allowed as a value to be read in from a Tempo-style .par file. The variable is defined to be an orientation angle in the pinned superfluid model of https://www.arxiv.org/abs/0909.4035. However, in .par file LAMBDA already has a meaning, which is the Galactic longitude of a pulsar. This MR does the following:

• it switches the parameter currently called LAMBDA to instead be called LAMBDAPIN and corrects the only use of this parameter (see https://git.ligo.org/lscsoft/lalsuite/-/blob/master/lalpulsar/lib/HeterodynedPulsarModel.c?ref_type=heads#L1295)
• it then reassigns LAMBDA to be the Galactic longitude and adds the ability to read in the Galactic latitude as BETA along with the proper motion in both ecliptic and Galactic coordinates. Note that I do not update the BinaryPulsarParameters structure to store these.

API Changes and Justification

Backwards Compatible Changes

• This change does not modify any class/function/struct/type definitions in a public C header file or any Python class/function definitions
• This change adds new classes/functions/structs/types to a public C header file or Python module

Backwards Incompatible Changes

• This change modifies an existing class/function/struct/type definition in a public C header file or Python module
• This change removes an existing class/function/struct/type from a public C header file or Python module

This is required to fix a name clash.

Review Status

cc @karl-wette @david-keitel